There you go I hope it helps
There are 6 other positions in the string, each with 26 choices. So if you fix BO as the first two letters, there are

possible strings that you can make.
If BO is at the end of the string, you still have

possible strings.
Together, then, you have

possible strings.
Answer:
You can see that each of the Oxygen atoms has eight electrons, and the two Hydrogen's have two electrons each.
Step-by-step explanation:
It's basically asking 75% of what number is 63 so x * 75% = 63
75% in decimal form is .75
divide 63 by .75 which is 84.
so 75% of 84 would be 63.