I need help with the whole of number 8

In priyas math class there are 10 boys and 15 girls. what is the ratio of boys to girls in priyas math class? express your answer as a decimal

If x varies directly as y, and x = 7.5 when y = 10, find x when y = 4

Two sides of a right triangle measure 2 units and 4 units. what is the area of the square that shares a side with the third side of the triangle?