10 person a buys 6 granola bars and 4 cups of yogurt for $10.50. person b buys 4 granola bars and 8 cups of yogurt for $11. find the cost of each item.

Let the cost of granola bars be G and the cost of a cup of yogurt be Y.
For Person A: 6G + 4Y = 10.50
For Person B: 4G + 8Y = 11
Multiply first equation by 2: 12G + 8Y = 21
Subtract this by the 2nd equation: 8G = 10
Divide by 8: G = 1.25
Substitute back into the first equation: 6(1.25) + 4Y = 10.50
Y = 0.75

So a granola bar costs $1.25 and a cup of yogurt costs $0.75

22.

Subtracting is the opposite of adding