Answer:
7
Explanation:
Try taking everything besides the x away. So the opposite of positive 7 is negative seven on the opposite side. 21-7 is 14 and 2x=14 is all that remains. The opposite of 2 times x is 2 divided by x and since we want to keep the x we divide the 2 on the other side, 14/2 is 7. x=7 is what remains.