9/10 (x + 8) = 18 ugh math hurts my head

The formula for the lateral area of a right cone is la = rs, where r is the radius of the base and s is the slant height of the cone. which are equivalent equations?

Let f(x) = 3 − x . find the average rate of change of f(x) from x = a to x = a + h and simplify your answer so that no single factor of h is left in the denominator.

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.