The area of a room is 396 square feet. the length is x+3, and the width is x+7 feet. find the dimensions of the room

This is an odd problem. The length and width look like they should be interchanged. Anyway I'll solve it and we'll talk about the results.
(x +7) (x + 3) = 396
x^2 + 7x + 3x + 21 = 396
x^2 + 10x + 21 = 396 Subtract 21 from both sides.
x^2 + 10x = 396 - 21
x^2 + 10x = 375
x^2 + 10x - 375 = 0 This probably factors.
(x + 25)(x - 15)
x + 25 = 0
x = - 25 which makes no sense. Negatives do not describe room dimensions.
x - 15= 0
x = 15. this is fine.

x+3 = 15 + 3 = 18
x + 7 = 15 + 7= 22

Check

Area = L * W = 18 * 22 = 496. It does check.
22 should be the length

18 should be the width.

What do you mean by that?