171 + 727 = 175 + 725 how do you come up with this in common core math

Abouncy ball is dropped such that the height of its first bounce is 5.5 feet and each successive bounce is 64% of the previous bounce's height. what would be the height of the 7th bounce of the ball? round to the nearest tenth (if necessary).

In a class, there are 12 girls. if the ratio of boys to girls is 5: 4 how many boys are there in the class

If the discriminant if a quadratic equation is 4 which statement describes the roots?