So to start since we are dividing the 2 fractions we can actually multiply the first fraction by the reciprocal of the second fraction. The reciprocal is just the fraction flipped so instead of 6/7 it will be 7/6.
3/5 x 7/6
Now we can multiply the numbers from left to right as you would in any other problem.
3/5 x 7/6 = 21/30
Since 21 can only go into 30 one time this fraction is in its simplest form already.
Answer: 21/30
Hope this helps :)