Answer:
\(y=10.5\)
Step-by-step explanation:
we have
\(x+y=12\) ------> equation A
\(x-3y=-30\) ------> equation B
Multiply by \(-1\) equation A
\(-1*(x+y)=-1*12\) -------> \(-x-y=-12\) ------> equation C
Adds equation B and equation C
\(x-3y=-30\\-x-y=-12\\ -----------\\-3y-y=-30-12\\-4y=-42\\y=42/4\\ y=10.5\)
