We can solve with a system of equations, and use c for the amount of cans of soup and f for the amount of frozen dinners.
The first equation will represent the amount of sodium. We know the (sodium in one can times the number of cans) plus (sodium in one frozen dinner times the number of dinners) is the expression for the total sodium. We also know the total sodium is 4450, so:
250c + 550f = 4450
The second equation is to find how many of each item are purchased:
c + f = 13
Solve for c in the second equation:
c = 13 - f
Plug this in for c in the first equation:
250(13-f) + 550f = 4450
3250 - 250f + 550f = 4450
300f = 1200
f = 4
Now plug the value for f into the second equation:
c + 4 = 13
c = 9
The answer is 9 cans of soups and 4 frozen dinners.
