can someone help me with part c on this question - i’ve done it but when i was marking it i wasn’t sure whether i would get a mark or not? i’ve attached the question, what i’ve done and the answer :)

can someone help me with part c on this question ive done it but when i was marking it i wasnt sure whether i would get a mark or not ive attached the question class=
can someone help me with part c on this question ive done it but when i was marking it i wasnt sure whether i would get a mark or not ive attached the question class=