Okay so.
We have two basic equations
Tower A+ B+720 A is 720ft taller than B.
Tower A+B= 1982 Combined height is 1982ft
Replace A with B+720 in 2nd equation and solve for B
B+720+B=1982 Combine like terms
2B+720=1982 Subtract 720 from both sides
2B=1262 Divide both sides by 2
B=1262/2
B= 631ft
We know that A=B+720 so you simply need to do that addition to have the height of both towers.