ASAP!!! Can someone help me with this I can’t understand it

Okay, so first, you have to figure out the values of a and b. In this case, you can use the fractions to figure out how many fourths would be equivalent to a certain amount of sevenths. Because you cannot divide seven into fourths, there is only one possible value for each variable.

A = 4
B = 7

Now, you just have to solve and simplify the fraction a-b/b

4-7/7
-3/7

Please take my advice with a grain of salt since I am not entirely sure if this is correct. But, if it is, I would really appreciate it if you could mark me as brainliest :)