Question

equação-9×-21=100-2× ? com conta

Answer 1

 9x - 21 = 100 - 2x 

9x + 2x = 100 + 21 

11x = 121

x = 121/11

x = 11               ok

Answer 2

-9x-21=100-2x
-9x+2x=100+21
-7x=121
x=-121/7