Just by comparing the plots of f(x) and g(x), it's clear that g(x) is just some positive scalar multiple of f(x), so that for some constant k, we have
g(x) = k • f(x) = kx² = (√k x)²
The plot of the transformed function g(x) = (√k x)² passes through the point (1, 4), which means
g(1) = (√k • 1)² = 4
and it follows that k = 4. So g(x) = 4x² = (2x)² and B is the correct choice.
