Note that f(x) = 2x² + 5x, and g(x) = 3x
Plug in 3x for x in f(x)
f(g(x)) = 2(3x)² + 5(3x)
Simplify. First square 3x
3x(3x) = 9x²
f(g(x)) = 2(9x²) + 5(3x)
Simplify. Multiply 2 with 9x², and 5 with 3x
2(9x²) = 18x² 5(3x) = 15x
f(g(x) = 18x² + 15x
f(g(x) = 18x² + 15x is your answer
hope this helps