So remember that area of a rectangle is a = bh. In this case, our sides are 2 and n - 3 (three less than unknown number) and our area is 22. Using our info, we can form the equation:
. From here we can solve for n.
Firstly, foil 2(n-3):

Next, add 6 on both sides of the equation:

Next, divide both sides of the equation and your answer will be 14 = n. In context, the value of the unknown number is 14 in.