Evaluate 1 2/3 x 2 5/8

Evaluate the expression for the given value of the variable 2×(c2-5) for c=4

How do i start to solve? would appreciate a walk-thru! a bird sitting 16ft above the ground in an apple tree dislodges an apple. after how many seconds does the apple land on the ground? (assuming that no branches will interfere with it's fall)

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