math
posted by danica .
the dimensions of a door are 3ft by 7ft 6in. if the same amount is added to each dimension of the door, the area is increased by 18ft^2. Find the dimensions of the new door. answer is supposed to be 4.5ft by 9ft need help asap

(3+x)*(7.5+x)  (3*7.5) = 18
Solve for x and then add to the original dimensions.