Let f(x)=25x2−2 . the function g(x) is a vertical stretch of f(x) by a factor of 2. what is the equation of g(x)?

For this case we have the following function:
 f (x) = 25x2-2
 Applying the transformation we have:
 To graph y = a * f (x)
 If a> 1, the graph of y = f (x) is expanded vertically by a factor a.
 We have then:
 g (x) = 2 * f (x)
 g (x) = 2 * (25x2-2)
 g (x) = 50x2 - 4
 
 The equation of g (x) is:
 g (x) = 50x2 - 4

Ithink the answer is b