我在星期五我有一個數學考試。 我不能可能準備，因為不懂/了解知道這個課題。 

現在沒有上這個課了，因此所以不需要有做好的得分數， 不過成績不好, 怕我夏課就不 /及/合/ 格了.  可是我想要學習。 但如果我現在不學習，這個夏天能失敗。

需要  = need an object  or noun.  

我需要水 = I need water

我需要你 = I need you

In other words, it means "need for something"

須要 = need <action or verb>

我須要你准批 = I need you to approve 

我須要你喝水 = I need you to drink water

須要有愛心    = need to HAVE love

Thus, "needs to do something".

Take a look in this case...

須要工作 or 需要工作.  This depends on the context.  Is 工作 is a verb or a noun.  If the English is "I need to work" then then the first one, otherwise, "I need to work" will be the second one.  Many Chinese native speakers make this mistake just like in English, "cannot" is the correct form while "can not" is wrong etc.  These are the quirks of languages.

I have a math test on Friday. I can not am unable to prepare, because I do not understand the subject.

I am no longer in the course (I no longer have the course), so it is not necessary to score well. But if I do not score well, I may fail the class in the summer.

我星期五有一個數學考試

我星期五有一個數學考試。 我不會準備，因為不了解這個課題(章節)。

現在我不再上這門課，所以不需要得到好的成績，可是我想要學習。 但如果我現在沒有得到好成績，這個夏天這門課會沒過。

I have a math test on Friday. I can not prepare, because I do not understand the subject(the chapters).

I am no longer in the course (I no longer have the course), so it is not necessary to score well. But if I do not score well, I may fail the class in the summer.

我(在)星期五有一個數學考試

我(在)星期五有一個數學考試。 我無法準備，因為我不懂這個課題。

現在我沒有修這門課，所以不需要得高分，可是我想要學習。 如果我現在不學好一點，在這個夏天的課可能就會沒過。

I have a math test on Friday. I can not prepare, because I do not understand the subject.

I am no longer in the course (I no longer have the course), so it is not necessary to score well. But if I do not score well, I may fail the class in the summer.

我在星期五有一個數學考試

我在星期五有一個數學考試。 因為不知道這個考试，所以我根本没做好准备or 复习。

現在（开始会）很长一段时间沒有这门课了，所以也不需要学得很好。但是我想好好学习（这门课程），如果我現在不（认真学好这门课程），這個暑假（这门课程）我可能考试失败or 考试不通过。

I have a math test on Friday. I can not prepare, because I do not understand the subject.

I am no longer in the course (I no longer have the course), so it is not necessary to score well. But if I do not score well, I may fail the class in the summer.