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.