Answers:
18. 2.5y-10.0=-0.5
move -10 to the other side
the sign changes from -10 to +10
2.5y-10+10= -0.5+10
2.5y= -0.5+10
2.5y= 9.5
divide by 2.5 for both sides
2.5y/2.5= 9.5
y= 3.8
19. 2(5-2z)=20-2(z-1)
Mutiply the first bracket by 2
(2)(5)= 10
(2)(-2z)= -4z
Mutiply the second bracket by 2
(-2)(z)= -2z
(-2)(-1)= 2
10-4z= 20-2z+2
10-4z= 20+2-2z - combine like terms
10-4z= 22-2z
move -4z to the other side
sign changes from -4z to +4z
10-4z+4z= 22-2z+4z
10= 22+2z
move 22 to the other side
10-22=22-22+2z
-12= 2z
divide both sides by 2
-12/2= 2z/2
z= -6
