Answer:
,
,
,
,
Step-by-step explanation:
First question:
He starts with 18, gains 2 every week, and needs 42. This means the equation is .
Second question:
He starts with 2, gains 18 every week, and needs 42. This means the equation is .
Third question:
It starts with 42, loses 2 every day, and needs 18. This means the equation is .
Fourth question:
Each friend has a total bill of 18+x, there are 2 friends, and they need 42. This means the equation is .
The only answer left is , so that's the answer to the fifth problem.