What is 9-j=10?

Problem:  9 - j  =  10.

Procedure:  get the variable alone on one side.

First:  remove 9 from the left side by subtracting 9 from both sides:  (9 - j) - 9  =  10 - 9

Simplify:  - j  =  1

To solve for j, we need to eliminate the - sign from the left side; multiply both sides by -1:

     -1( -j )  =  -1(1)

Simplify:  j  =  -1

What is 9-j=10

-j=10-9 we move all numbers to one side and change the sign from + to -

-j=1 we multiply both sides by -1

j=-1 which your answer, because: 9 - (-1)=10=9 + 1=10