Question

Paul is solving an equation on the bottom of a page. His pen breaks, and ink spills on the corner of the page where the equation is written, as shown.
Paul knows only one number or expression is covered by the ink stain, and he knows that the equation has a solution of 6. What must be the covered number or expression?

A. 3
B. 3x
C. 6x
D. 6

Answer 1

Answer: Option B

Step-by-step explanation:

If the solution is 6 then it means that x=6.

Let's call the missing number y

Substitute x=6 and y into the equation and solve for y:

$6(6+4)=6(6+7)-y\\6(10)=6(13)-y\\60=78-y\\y=78-60\\y=18$

The options does not show 18, but the option B shows 3x, then if x=6:

$3x=3*6=18$

The answer is the option B