A hot dog has about 1/4 the amount of protein as 3 ounces of hamburger. Together, they have about 25 grams of protein. How many grams of protein are in a 3 oz hamburger?

(1) protein in hot dog = ¼ * protein in 3 ounces of hamburger

(2) protein in hot dog + protein in 3 ounces of hamburger = 25

So we need to re-arrange (1) and (2) to solve for the protein in 3 ounces of hamburger!

(re-arrange (1)): 4 * protein in hot dog = protein in 3 ounces of hamburger

(re-arrange (2)): protein in hot dog = 25 - protein in 3 ounces of hamburger

(plugging re-arranged (2) into re-arranged (1)):

4 * (25 - protein in 3 ounces of hamburger) = protein in 3 ounces of hamburger ( multiplying )

100- 4 protein in 3 ounces of hamburger = protein in 3 ounces of hamburger

solving for the protein in 3 ounces of hamburger:

5 * protein in 3 ounces of hamburger = 100

protein in 3 ounces of hamburger = 20 gram

-2

7 - 9 = -2

reversed:

-2 + 9 = 7