First you want w on a side by itself. So you divide w by 3.50 and divide 84 by 3.50. And 3.50 on the left side cancels out. And then you are left with w = 24.
Answer is B Reason 3 times he eats lunch for $3.50 for each lunch so (3x$3.50) is total for each week Using w for the unknown amount of weeks Now finish the equation (3x$3.50)w = $84