The ratio of red peppers to green peppers is 3:4, which means for every 3 red peppers, there are 4 green peppers.

If the truck contains 120 green peppers, we can use the proportion to find the number of red peppers.

120 peppers / 4 peppers = x peppers / 3 peppers

We can cross-multiply and solve for x:

120 peppers * 3 peppers = 4 peppers * x peppers

x peppers = 120 peppers * 3 peppers / 4 peppers

x peppers = 90

So, there are 90 red peppers in the truck.

In total, there are 90 red peppers + 120 green peppers = 210 peppers.