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Explanation:
To isolate 'e', we can add it to both sides like so
d-c-e = 17
d-c-e+e = 17+e
d-c+0e = 17+e
d-c+0 = 17+e
d-c = 17+e
The 17+e is the same as e+17. We can also flip both sides to get the equation
e+17 = d-c
From here, we need to undo that +17. So we subtract 17 from both sides to fully get 'e' all by itself.
e+17 = d-c
e+17-17 = d-c-17
e+0 = d-c-17
e = d-c-17
If we knew the values of c and d, then we could find the numeric value of 'e'. But we don't have enough information.
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In short, you add 'e' to both sides and you subtract 17 from both sides to get e = d-c-17
