When 3/4 of a cup is doubled, the result are 1 1/2 cups. When adding like fractions, the bottom number, the denominator, remains the same. In this case, it is four. The top numbers, or numerators, are added.
Adding the numerators, three and three, yields six. The resulting fraction is 6/4. The next step is simplifying this fraction. The numerator is greater than the denominator and this indicates that the answer is more than one. Therefore, the numerator is divided by the denominator, which equals one with a remainder of two. This remaining fractional part, 2/4, is simplified by dividing both numerator and denominator by the greatest common factor, which is 2. This becomes 1/2, for a final answer of 1 1/2.