Colleen is knitting a scarf. For every 45 pieces of blue yarn she uses, she uses 18 pieces of red yard. What equation can be used to represent the proportional relationship between the amount of blue yarn, b, and red yard, r, that Colleen uses when knitting a scarf?

The equation that can be used to represent the proportional relationship between the amount of blue yarn, b, and red yarn, r, that Colleen uses when knitting a scarf is:

or

Step-by-step explanation:

In the exercise are given the variables that we must use in the equation: b and r, where b is the amount of blue yarn and r is the amount of the red yarn, now it's just missing the proportion that must be used in the equation, to identify this you only must divide the biggest amount (45) by the smallest amount (18), how I show below:

Having this, you can make the equation taking into account the proportion:

This equation marks that by each piece of blue yarn, are needed 2.5 pieces of red yarn, we can prove the equation replacing the r-value by 18:

How you can see, replacing the r-value by 18, the value given for red yarn, we obtain the value given for the blue yarn: 45.