Answer:
4/7
Step-by-step explanation:

X+3=15 = x+3-3=15-3
you need to isolate the variable... x
so now it is x=12
hope that helped!
Add all the numbers in the list then divide it by how many numbers are in that list. Ex. 5,8,1,4 Would be: 5+8+1+4= 18 divided by 4 which is 4.5