Step-by-step explanation:
The answers are proved by replacing x with 3 and 6 respectively.
W+D=659
W=D-91
---------------------------
(D-91)+D=659
D-91+D=659
2D=750
D=750/2=375
------------------------------
W+375=659
W=284
------------------------------
So the dryer had cost $375 and the washer had cost $284.