Byron S. answered 10/14/14
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Math and Science Tutor with an Engineering Background
Let x be the number of $17 trophies.
Let y be the number of $32 trophies.
Let z be the number of $49 trophies.
There are a total of 35 trophies:
x + y + z = 35
The total cost is $1285
17x + 32y + 49z = 1285
He needs 8 fewer of the $17 trophies than of the $32 trophies
x = y - 8
These three equations are your system. You can use the third and substitute into the first two to eliminate x and simplify:
(y-8) + y + z = 35
17(y-8) + 32y + 49z = 1285
From here, combine like terms and simplify. You now have two equations with two unknowns, and can solve relatively easily using either the substitution or elimination methods. I'll leave that up to you.
If you have further questions, please comment.