Hello, pay attention: You have a fraction 6/8.
You can make it bigger or smaller by multiplying or dividing both values with the same number.
In this case, you are given that in the new fraction, the number below, which is 4.
That number is corresponding to the number below in given fraction 6/8, and now, we need to see how many times is number in the new fraction bigger or smaller than in the given fraction.
We can clearly see that 4 is 2 times smaller than 8, so we need to divide each number in a fraction by 2, so the new fraction is : 6/2 = 3 and 8/2 = 4 => 3/4.
Hope this helps!