What is the ratio of 15 and 40 in simplest form

What is the value of  y  in the solution to the system of equations? x  +  y  =  12x  –  3y  =  –30a. –8b. –3c. 3d. 8

Which of the following represents a number squared is equal to twenty more than nine times that number ? a) x squared = 9x + 20 b) x squared = 20x + 9 c) x squared > 9 + 20x d) x squared = 9 + x + 20

Prove sin2a + cos2a - 1 / sin2a + cos2a + 1 = 1 - tana / 1 + cota