Solve for x:
15).
x - 50 = 49
16).
x - 125 = 375
17).
x - 50 = -25
18).
x - 90 = - 30
19).
x - 197 = 0
20).
x + 128 - 256 = 64 (two steps)
21).
Chang has 43 comic books left in his collection. Last week he gave 10 of them to Anne and 5 to Matt. How many comic books did he start with. Let x be the number he started with. Write the algebraic equation and solve for x.