A bag contains 120 marbles. Some are red and the rest are black. There are 19 red marbles for every

A bag contains 120 marbles. Some are red and the rest are black. There are 19 red marbles for every black marble. How many red marbles are in the bag?

Let the red marbles be r
Let the black marbles be b.

A 19 to 1 red to black is written as:
r = 19b

We're also given:
b + r = 120

Substitute r = 19b into this equation and we get:
b + 19b = 120

Combine like terms:
20b = 120

To solve this equation, we type it in our search engine and we get:
b = 6

Since r = 19b, we substitute b = 6 into this equation to solve for r:
r = 19(6)
r = 114