To subtract fractions, you first need to find a common denominator. The common denominator should be a multiple of both denominators. We can use 30 because it is a multiple of both 10 and 3.
Now that we have 30 on the bottom, we need to multiply the numerators by the same amount we multiplied the denominator by to keep the fractions proportional.
First 7/10... To turn 10 into 30 we had to multiply by 3. Do the same to the 7. We now have 7*3 = 21.
Then -5/3... To turn 3 into 30 we had to multiply by 10. So -5*10 = -50.
