Explanation:
Four containers of pudding cost $4.20.
4x = 4.20
x = 1.05
Using this we know that one container of pudding costs $1.05.
Then, divide the maximum amount that you have by the cost of one.
9.45/1.05 = 9
With $9.45, you can buy nine cups of pudding.
In the case that you can buy the four containers in bulk (4 at a time)...
You can only buy 8 containers of pudding (two) because $4.20 only fits into $9.45 twice.