Area of pavillion = x * 3x
Area of pavillion + walkway = (x+6) * (3x+6)
Area of walkway = (area of pavillion + walkway) - area of pavillion = 396 ft^2
(x+6)(3x+6) - (x*3x) = 396
3x^2 +24x +36 - 3x^2 = 396
24x = 360
x= 15
Pavillion = x * 3x = 15 x 45 ft dimensions
Area of walkway = 396 ft^2 (given)