313
This is just like 91 - 78 with the 300 along for the ride. Subtraction means distance on the number line. From 78 to 80 is 2, from 80 to 90 is 10, and from 90 to 91 is 1. That difference is 91 - 78 = 2 + 10 + 1 = 13. Add the 300, and we have 313.