Answer :

[tex]3.5r=3(4+0.5r)\\\\3.5r=3\times4+3\times0.5r\\\\3.5r=12+1.5r\ \ \ \ \ |substract\ 1.5r\ from\ both\ sides\\\\2r=12\ \ \ \ \ \ |divide\ both\ sides\ by\ 2\\\\r=6[/tex]
AL2006
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

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