At a corner gas station, the revenue r varies directly with the number g of gallons of gasoline sold. if the revenue is

At a corner gas station, the revenue R varies directly with the number g of gallons of gasoline sold. If the revenue is $44.50 when the number of gallons sold is 10, find a linear equation that relates revenue R to the number g of gallons of gasoline. Then find the revenue R when the number of gallons of gasoline sold is 15.5.

Solution:
As the question mentioned the direct relationship between the quantities, hence 
10 gallons of gasoline sold =  $44.50
15.5 gallons of gasoline sold = $x
by cross multiplication, we get that
10x = 15.5 * 44.50
which implies that
x = 68.975
Thus by $68.975 revenue is obtained by selling 15.5 gallons of gasoline.

The answer would be b