Question

Robert sells 3 packages of cookie dough and 8 packages of pie dough for $35. Phil sells 6 packages of cookie dough and 6 packages of pie dough for $45. How much does each type of dough cost?

Answer 1

Cookie dough: `$5`
Pie dough: `$2.5`

Explanation:

Just for shorting will call the cookie dough `(x)` and the pie dough `(y)`.

We know Robert sold `3x+8y` for 35, and Phil sold `6x+6y` for 45.
To try to get to how much each cost, we need to put aside one of 'dough'; we do so by making one of the doughs even and then eliminate it (for now)

`(3x+8y=35)" "xx(-2)`

And if we put them together and subtract one by one,

`-6x-16y=-70`

`6x+6y=45`

We get

`(-10y=-25) " ":(-10)`

`y=2.5`

Now we can return to the dough we left aside. And this time we already know how much pie dough cost so we put this, in case of Phil `6xx2.5=15`

And we left with this

`(6x+15=45) -15`

`(6x=30)" " :6`

`x=5`