Answer:
He made 42 cookies and 30 brownies.
Explanation:
Let c = number of cookies
Let b = number of brownies
"He made 12 more cookies than brownies."
The number of cookies is 12 more than the number of brownies.
c = b + 12
"He sold cookies for $1.50 and brownies for $2."
The money he made from selling cookies was 1.5c.
The money he made from selling brownies was 2b.
The total sales were $123
1.5c + 2b = 123
We have a system of equations.
c = b + 12
1.5c + 2b = 123
Substitute c of the second equation with b + 12
1.5(b + 12) + 2b = 123
1.5b + 18 + 2b = 123
3.5b = 105
b = 30
c = b + 12
c = 30 + 12
c = 42
He made 42 cookies and 30 brownies.