Part A
You know that 1 bag of candy weighs 5 pounds.
Elijah has 1/2 (half) bag of candy, to determine how much the half of a bag weight, you have to multiply the weight of a whole bag by 1/2:

Divide the whole number by 1 to express it as a fraction and multiply both fractions:

Elijah has 2.5 pounds of candy.
Part B
Now he has 2 1/2 bags of candy, as before, to determine how many pounds he has, you have to multiply this amount by the weight of one bag:

-First, you have to express the mixed number as an improper fraction:
1) Divide the whole number by one to express it as a fraction and add the fraction:

2) Multiply the first fraction by 2 to express it with denominator 2

-Second, multiply 5/2 by 5

Elijah has 12.5 pounds of candy.