2[s + 3(s - 1)] = 18
Do the parenthesis because of using PEMDAS.
P=parenthesis
E= exponents
M= multiplication
D= division
A= addition
S= subtraction
(3)(s)=3s
(3)(-1)=-3
2 [ s+3s-3)] =18
2 [4s-3]=18
Multiply the bracket by 2
(2)(4s)=8s
(2)(-3)=-6
8s-6=18
move -6 to the other side
sign changes from -6 to +6
8s-6+6=18+6
8s=24
divide by 8 for both sides
8s/8=24/8
Cross out 8 and 8, divide by 8 and then becomes 1*1*s=s
s=3
Answer: s=3