Answer:in the resulting recipe, 2 onions were used and 11.5 tomatoes were used.
Explanation:
Let x represent the number of onions used.
Let y represent the number of tomatoes used.
The recipe states that four times the number of tomatoes, , plus five times the number of onions should produce 56 bowls of tomato soup. This means that
5x + 4y = 56 - - - - - - - - - - - - -1
A different recipe states that two times the number of tomatoes used minus the number of onions used should produce 21 bowls of tomato soup. This means that
2y - x = 21
-x + 2y = 21 - - - - - - - - - - - - - - 2
Multiplying equation 1 by 1 and equation 2 by 5, it becomes
5x + 4y = 56
-5x + 10y = 105
Since the two recipes were added together, we would add both equations. It becomes
14y = 161
y = 161/14 =11.5
Substituting y = 11.5 into equation 1, it becomes
-x + 2 × 11.5 = 21
-x + 23 = 21
-x = 21 - 23 = -2
x = 2