To solve for the x, distribute first the numerical coefficients to the terms on the parentheses. This becomes,
7x - 21 = 4x + 20
Transpose all the terms with x and the constant on either sides of the equation,
7x - 4x = 20 + 21
3x = 41 ; x = 41 / 3
Thus, the answer is x = 41/3 which is fourth among the choices.