Don has one-third as much money as Ann. Gwen gives Don $17.

Now Ann has $2 less than Don. How much money do Ann and
Don have in all?

is this how to set it up?
t = 1/3 g +17
g = t - 2

who knows, you haven't defined those variables.

Who or what is t

Here is how I would set it up:
let Ann's amount be x
then Don has (1/3)x
he also gets $17 from Gwen, (wherever she came from)

No now Don has (1/3)x + 17
This is now $2 more than what Ann has, so

(1/3)x + 17 - x = 2
times 3
x + 51 - 3x = 6
-2x = - 45
x = 22.5

so together they would have 22.5 + 7.50 = ....

check:
Ann now has $22.50
Don has a third of that , so has $7.50
he gets an additional $17 , so now he has 24.50

Does Ann have $2 less than Don??? YES