To multiply a whole number by a fraction, you have to change the whole number (the 3) into a fraction. To do this, simply put the 3 over 1.
3/1 x 7/8. Multiplying fractions is so easy because all you have to do is multiply the numerators together and then the denominators together.
3x7=21
1x8=8
21/8
This fraction cannot be reduced, but it can be rewritten as a mixed number.
21 divided by 8 is 2 with a remainder of 5.
The answer is 21/8 or 2 5/8. (they mean the same thing)