The answer is a; 4/3
This is because you are dividing fractions. When dividing, you flip the second fraction (keep, change, flip). You keep the first fraction (6/7). Change the division sign to multiplication and flip the second fraction from 36/56 to 56/36. Then you cross multiply, 6/7 x 56/36. And simplify by dividing both the numerator and denominator by a number they both go into evenly.
