Let the prior percentage be [tex]x[/tex]
If we add 11.7% to [tex]x[/tex], we get 51.3%.
That is [tex]x+11.7%=51.3%[/tex].
This is a linear equation in [tex]x[/tex], so we solve for x to obtain,
[tex]x=51.3%-11.7%[/tex]
[tex]x=39.6%[/tex]
Therefore the prior percentage was 39.6%
