Question 281440
The side of one square is 5 units longer than that of another square. Their areas differ by 105 square units. The lengths of their sides are: 
(A) 5 and 10 units (B) 7.5 and 12.5 units (C) 8 and 13 units
(D) 15 and 20 units (E) none of these 


Let x be the length of the sides of the smaller square. Then x+5 is the length of the sides of the larger square. Then the areas of the squares are x^2 and (x+5)^2 respectively.

So we have:

(x+5)^2 - x^2 = 105

Expanding using FOIL gives us:

x^2 + 10x + 25 - x^2 = 105

10x + 25 = 105

Solve for x and calculate x+5.