Step-by-step explanation:
using elimination method because this is a simultaneous equation
3×x+6×y=111
x+y=27
1×[3x+6y=111]
3×[x+y=27]
3x+6y=111—equation 1
3x+3y=81—equation 2
substrate equation 1 from equation 2
3y=30
divide both sides by 3
y=10
substitute 10 for y in equation 1
3x+6y=111
3x+6(10)=111
3x+60=111
3x=111-60
3x=51
divide both sides by 3
x=17