Currently, there are about 850 calories in two slices of pizza. This is 150 calories less than twice the number of calories in two slices 20 years ago. How many calories were in two slices of pizza twenty years ago?

A) 850 - 2x = 150
B) 850 - 150 = 2x
C) 850 = 150 - 2x
D) 850 = 2x - 150