Expand then sliplify : 3z (2z +4) + 6z (2z - 5)

Ineed with this problem 21 show steps

How do i simply this expression (quadratic formula basis) on a ti-84 or normal calculator?

The point of intersection of the diagonals of a rectangle is 4 cm further away from the smaller side then from the larger side of the rectangle. the perimeter of the rectangle is equal to 56 cm. find the lengths of the sides of the rectangle. 16 points answer quick