Hi Jay,
Well the first order suggests the equation:
2H + 5D = 8 H is a hamburger, D is a hot dog
The second order suggests the equation:
5H + 2D = 9.5
Suppose make the first order twice, so the total order is:
4H + 10D = 16
And we make the second order 5 times, then it's total order is:
25H + 10D = 47.5
Now, each of the orders has 10 hot dogs. Let us subtract the smaller order and cost from the other. It leaves
21H = 31.5 Then Divide by 21
H = 1.5
A hamburger costs $1.50
This is called the elimination (or sometimes addition) method of solving a system of equations. The trick is choosing to multiply each order by a number that will leave you with a number of, in this case, hot dogs, that is the same as in the other order.