To solve the equation \( x \div 12 = 40 , \text{R} , 7 \), we first need to understand what "40 R7" means. It indicates that when \( x \) is divided by 12, the quotient is 40 and the remainder is 7.
We can express this relationship in the form of an equation:
\[ x = 12 \times 40 + 7 \]
Calculating this:
\[ x = 480 + 7 = 487 \]
Thus, the number that makes the equation true is \( \boxed{487} \).