Question

How can I express the area of the blue tiles?

Answer 1

The area of the blue tiles is the area of the entire design minus the area of the green tiles, or B = A - G

For the next question,
A = 49 in^2 
G = 15 in^2

B = 49 - 15
B = 34 in^2

Answer 2

7x7 minus 5x3 would get you the blue