Let green peppers = g, let red peppers = r.
g = 4r
g + r = 20
Plug in 4r for g
4r + r = 20
Simplify. Combine like terms
4r + r = 20
5r = 20
Isolate the r. Note the equal sign. What you do to one side, you do to the other. Divide 5 from both sides
5r/5 = 20/5
r = 20/5
r = 4
There are 4 red peppers.
Plug in 4 to one of the equations
g = 4r
g = 4(4)
g = 16
There are 16 green peppers.
Answer: 4 red peppers, 16 green peppers
hope this helps