Write the equation for a line passing through (4, 13) and has a slope of 3

Tyler enjoys the fish so much that after his birthday his family decides to take him to a famous aquarium a tank at the aquarium is similar to his tank with the scale factor of 8 how many times greater is the volume of the tank at the aquarium than the volume of tyler tank

Ineed i been stuck on this question since yesterday

If cos(2x) = tan^2(y), show that cos(2y) = tan^2(x).