Use cross multiplication to answer this. Since there is 2.5 grams in 1 serving, you would set it up with grams of fat being the numerator and servings being the denominator, like this:
2.5 / 1 = x / 3.75
Then just do the algebra:
(2.5 / 1) * (3.75) = x
And the answer is:
9.375 = x