area of rectangular post card = length x width
For the given post card:
length = 4 in
width = (3+b) in
area = 24 in^2
So, substituting in the equation of the area:
24 = 4 x (3+b)
24 = 12 + 4b
24 - 12 = 4b
12 = 4b
b = 3 in
Therefore:
the length of the postcard = 4 inch
the width of the postcard = b+3 = 3 + 3 = 6 inch
