A sign is being painted that includes 3 small squares with a side length of s and 2 large ones with a side length of S. Write an expression to find the total area of the sign that needs to be painted.

a. 3S^2+2s^2

b. 2S^2+3s^2

c. 2S^2-3s^2

d. 3S^2-2s^2