Hi! Look, it can be with　簡単「A な Adjective」、Or, with 易しい「An い Adjective」 When you negate an い Adjective, it has an own negative form: ・この宿題は易しくないです。 易しい Changes to 易しくない。When you wanna transform to negative an い Adjective you have to delete the last い and change it to くない instead. You don't have to put ではありません、Just put です、Because the ~くない Is denying the sentence. Also, you can use 簡単 That is a な Adjective so you can do it how you're doing it. ・この宿題は簡単ではありません。 *How Sento said, "deha" (dewa) is with particle は, not with わ *Sorry my bad English!!!! :( I hope you'll understand (:

hello! もう少しです！ この宿題は簡単ではありません。 この宿題は　簡単では　ありません(konoshukudaiwa kantandewa arimasen)