To solve this problem all you need to do is to combine like terms. Like terms are terms with the same variables (for ex. 4x and 6x, 3y and 9y) and powers (for ex. e^2 and x^2).
Start by writing out the entire problem to be well organized and make it easier to see if you were to do this with pen and paper.
(10j - 7) - (-9j + 2)
Distribute the negative sign into everything inside of the parentheses on the right hand side. Rewrite the problem again (preferably after every step to make it easier to catch a mistake you made if you were to double check your work).
(10j - 7) + 9j - 2
Finish off this problem by combining like terms. Add 10j and 9j together, and also add -7 and -2 together. Your final answer should look like this:
19j - 9