Answer:
(3,5)
Explanation
3=e and 5=f (but I guess u accidentally put a plus sign)
so 2e= 6 and 3f=15, and 6-15=-9 so this checks out
Next e=3 and 3f=15 (that 5 in the second problem should be an f) and 3+15-18 again is checks out so 3,5 must be correct yada yada yada goodnight.
-I'm usually more professional explaining problems but i broke it down for ya, when I get over this drowsiness I'll be back to my usually math pro self