This is a systems problem. Two variables to find. ( I assume that 2 and 3 means dollars )
S = sodas
D = hot dogs
S + D = 3000
2S + 3D = $7000
We will use substitution with the top equation.
D = 3000 - S
------Now, substitute this into bottom equation
2S + 3(3000 - S) = .7000
2S + 9000 - 3S = 7000
- S = - 2000
S = 2000
------Sodas are 2000 in number sold.
So, 1000 hot dogs were sold.