How do I do this problem

Answer:
The Ross family used it for 15 hours
The Watson family used it for 20 hours
Step-by-step explanation:
We can rewrite this word problem using variables.
[tex](x*40)+(y*20)=1000[/tex] and [tex]x+y=35[/tex]
Now we can split 35 between x and y. Since 35 can't be split into a whole number, I have split it into 17 and 18
(17*40) + (18*20) = 1040
This is close but 40 too much. Since this is 40 off, we need to move 2 more hours to the Watson family.
(15*40) + (20*20) = 1000
This means -
The Ross family used it for 15 hours
The Watson family used it for 20 hours