The ratio of tacos to salsa are 4 to 2, that is the proportion is:
In order to determine how many salsa will you get for 20 tacos, you take into account that the proportion must be the same indeoendently of the number of tacos.
Then, if x is the salsa, the proportion of 20 tacos to x salsa is:
To knoe the amount of salsa you solve for x. You multiply both sides by x and then divide both sides by 2, just as follow:
Hence, the amount of salsa present in 20 tacos is 10