How do I rewrite the expression as a single fraction?

6/7 - 2/5

Find a common denomenator

the easiest way is to multiply each by 1 or x/x where x=x

multiply 6/7 by 5/5 and multiply 2/5 by 7/7

we get

6/7-2/5=30/35-14/35 = (30-14) / 35=16/35