Fine the average of these numbers, 8,12,13,15

Two planes leave an airport at the same time, one flying east, the other flying west. the eastbound plane travels 20 mph slower. they are 1600 mi apart after 2 hr. find the speed of each plane.

The multiplicative property of equality states that for real numbers a, b, c, and d, if a = b and c = d, then ac = bd. true false

Prove that (x-2)is factor of p (x)=2x³-3x²-17x+30