What is the answer 3.5r=3(4+.5r)?

The 'answer' is the number that 'r' must be in order to make the equation a true statement.  There's only one number that can do it.  Here's how to find it:

Copy the equation:              3.5r = 3(4 + .5r)

Expand the right side:          3.5r = 12 + 1.5r

Subtract 1.5r from each side:  2r = 12

Divide each side by 2 :            r = 6

Your answer should be “c” mark me brainliest