Question

3a^2+4b^2 for a=2 and b=3

Answer 1

3a^2+4b^2

3(2)^2+4(3)^2

3(4) + 4 (9)

12+36 = 48

Answer 2

First write the question:
3a^2 + 4b^2

Substitute:
3 x (2^2)  +  4 x (3^2)

Simplify:
(3 x 4) + (4 x 9)

Simplify again:
12 + 36

Answer:
48

Hope it helped :)