How do you solve a 3 X 3 magic square when using 11-19 and 15 is in the middle square?

Try reading that thread:

https://www.askmehelpdesk.com/mathematics/3x3-magic-square-solver-471125.html

:)

Put 11 instead of 1.

-16, -12, -8, -4, 0, 4, 8, 12, 16