My first number is -2, my fifth number is 26
What is my third number?

Firstly, Subtract the smallest number from the largest number

26 - - 2 = 28

28 spans over 5 numbers so we divide it to figure out the difference between each number

28 / 5 = 5.6

-2 is the 1st number

+5.6

3.6 is the 2nd number

+5.6

9.2 is the 3rd number

lockers 1, 4, 9, 16, 25, 40, and 49 are open

i ran through it by the other answer is wrong