Answer:
Third option is the right choice.
Step-by-step explanation:
Manipulate the right hand side.

Best Regards!
Answer:
12 years old.
Step-by-step explanation:
1) 2x+x=18
2) Now solve 2x+x=18
Add alike terms
3x=18
Now divide both sides by 3 (3x/3 and 18/3)
x=6
So Hannah is 6 years old. Her sister must be 12.
Answer:
b = 12
Step-by-step explanation:
b/3 + 4 = 8
subtract 4 on both sides
b/3 = 4
multiply 3 with 4
b = 12
Answer:
108
Step-by-step explanation:
You are correct for stating one tissue box has a volume for 36.
But notice there are 3 tissue boxes, so in order to find the total volume, you should add them up.
36+36+36=108
500/20 = 25kcal per piece
8 * 25 = 200kcal.....yes, he is able to have 8 pieces