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

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 on class=