Which number replaces the box to make this a true sentence? 6 × (4 + 9) = 24 + a. 78 b. 54 c. 28 d. 13

I might be right but i dont even know... im pretty sure you use PEMDAS. Parentheses, Exponents, Multiply, Divide, Add, and Subtract. you go in those orders first the parentheses. 4+9= 13. so 6x(13). 6x13 is 78. so im pretty sure the awnser is 
A. 78.