HELP?? If r varies directly as s, and r = 39 when s = 26, find s when r = 21

Given the equation f(x)=a(b)x where the initial value is 40 and the growth rate is 20% what is f(4)

Which of the expressions (on the photo document i inserted) together represent all solutions to the following equation? 8cos(12x)+4=-4 *the answer should be in degrees.* > i would like for someone to explain the process to find the solutions for this.

For problems 29 - 31 the graph of a quadratic function y=ax^2 + bx + c is shown. tell whether the discriminant of ax^2 + bx + c = 0 is positive, negative, or zero.