Question 808309
You are being asked to find the unknown number, which we're going to call x. Therefore, you can write your equation the following way:

(x-7)*3=-9 or 3(x-7)=-9

Step 1: 3(x-7)=-9
Step 2: 3(x-7)/3=-9/3
Step 3: x-7=-9/3
Step 4: x-7=-3
Step 5: x+(-7+7)=-3+7
Step 6: x=-3+7
Answer: x=4

Hope that helped. :)