Your first one is incorrect, I think. Take the derivative first, without plugging in numbers. What do you get?
Your second one is confusing. I'm not sure what you mean on the LHS of the equals sign.
hi , thanks for the quick reply,. sorry about the equation the bit befoere the = sgn should be i , because the answer is electrical current, and as for the first one im not sure on the answer, i cant rmeber from the exam. i thnik ill just have to wait to august to find out, but thanks for the reply , i appreciate it