Question 7545
Can you verify that the problem was written correctly?  
You wrote: 4(Sn-7)=10n+2
Is it possibly: 4(5n-7)=10n+2?
If so, this is what you'd do:


1) Look at the first part "4(5n-7)"
you need to multiply 4 to both "5n" and to "-7"
(5n)(4)-(7)(4)

 
2) put it back into the equation:
4(5n-7)=10n+2
(5n)(4)-(7)(4)=10n+2
20n-28=10n+2


3) Subtract 10n from both sides to isolate +2
(20n-28)-10n=(10n+2)-10n
10n-28=2


4)add 28 to both sides to isolate 10n
(10n-28)+28=(2)+28
10n=30


5) divide both sides by 10 to isolate n
{{{(10n)/10}}}={{{30/10}}}
n=3