20 and 3/4 is 20.75
20 and 7/8 is 20.875
20 and 1/5 is 20.2
20 and 4/5 is 20.8
Plug in the second equation into the first equation for y.

Now put the variable on one side and constants on the other

Now plug that back into one of the original equations

So now you know

Its always a good idea to check