Please help with these high school geometry circle questions.

Suppose a gym membership has an initial enrollment fee of $75 and then a fee of $29 a month. which equation models the cost, c, of the gym membership for m months?

Bob the builder is making 480kg of cement mix. this is made by cement, sand and gravel in the ratio 1: 3: 4

What is the point of inflection for the function f(x)=2cos4x on the interval (0, pi/2)