Let's have X represent the number of red peppers Meredith picked:
X = red peppers
We know that Meredith picked 4 times as many green peppers as red peppers, so based on this:
green peppers = 4*(red peppers) = 4X
In total, she picked 20, so:
Red peppers + Green peppers = 20
X + 4X = 20
5X = 20
X = 4
So, Meredith picked 4 red peppers and 16 (4 times 4) green peppers!