Help me with maths :)

We just started the introduction into circles and i have no idea how to do this.

1) you deposit $2,500 in an account that earns 4% simple interest. how much do you earn in eight years?

Which sum or difference identity would you use to verify that cos (180° - q) = -cos q? a.) sin (a -b) = sin a cos b – cos a sin b b.) cos (a -b) = cos a cos b – sin a sin b c.) cos (a -b) = cos a cosb + sin a sin b d.) sin (a + b) = sin a cos b + cos a sin b