Alright, first thing's first, simplify the equation as much as you can. If you wanted, I suppose you could just multiply everything by 40, but that's super unconventional.
7x/8 - 3x/8 = 1/5 + 3/10
Simplify:
4x/8 = 1/5 + 3/10
Make sure that when subtracting or adding fractions that the denominators (The number on the bottom of the fraction) are equal.
In order to add 1/5 and 3/10 together, all we have to do is ensure that both denominators are equal.
To do this, simply multiply 1/5 by 2/2. The new fraction will be 2/10 (You can do this since it's the exact same fraction, 2/10 will simplify down to 1/5. The reason we did this was to make sure that the two fractions had equal denominators).
Our equation now looks like this:
4x/8 = 2/10 + 3/10
Add the fractions on the right:
4x/8 = 5/10
Huh, whaddya know? Both the fraction on the left and the right can be simplified into 1/2! (4/8 becomes 1/2, and 5/10 becomes 1/2)
1x/2 = 1/2
x/2 = 1/2
If you want to, I suppose you could cross multiply to check, but the answer's already pretty obvious.
x = 1
Good luck! If you need me to explain anything I did here, just ask :))
-T.B.