Answer:
N = D * 1.20
Explanation:
In order to calculate the number of dishes that the previous menu had we first need to turn this percentage into a decimal by dividing it by 100
20% / 100 = 0.20
Now we add a 1 to it since we are increasing the old menu by this amount
0.20 + 1 = 1.20
Now we can multiply this by the previous menu dishes (D) to get the new amount of menu dishes (N)
N = D * 1.20