Answer:
y= -2
Step-by-step explanation: x-10=0 move the - 10 to the other side it will be +10 s0 x=10
then use that value to solve the second equation
3*10 +5y=20
30 +5y=20
remember: anything that moves to the other side of the equation always invert its sign so +30 will be -30
5y= 20-30
5y= -10
y= -10/5
y= -2