Im not a very good mathematician, and im only in grade 10..and need some help

Question is: Show

sin(180-sinB)

____________ = -tanB

cos(180-B)

Sorry if this question is really easy, i must really suck.

Ive tried doing it:

sinB

____ = tan B

cosB

.: sin B- sinx

___________ = -tanx

cos B- cosx

Is this method right, and in an exam will i get full marks for it?

Another question:

Simplify cos(90-b)

_________

sin(180-b)

I havent the slightest idea what to do.

I understand that cosx over sinx= 1/2 x tanx..but the values of cos and sin are different in this question... so is it implying that the answer is:

cos90- cos b

_____________ = 1/4 x tan (since cos over sin is 1/2tan, this is half)

sin 180- sin b

And i need to solve for b....

Thanks in advance.