The answer is a. 19 x(42 + 58). In the expression 19 * 42 + 19 * 58, the common factor is 19. So, it can be taken out and the other factor of each binomial can be put into parenthesis. The general form will be: x * a + x * b = x * (a + b) where x is the common factor. In our expression: 19 * 42 + 19 * 58 = 19 * (42 + 58).