If Chris and Lisa went shopping and spent a total of $25.50 and Lisa spent $13.50 more then Chris spent. How much did Lisa spend?
\(x-\ Lisa\\ y-\ Chris\\\\ x+y=25.50\\ x-13.5=y\\\\ x+x-13.5=25.50\ \ \ | add\ 13.50\\\\ 2x=39\ \ \ | divide\ by\ 2\\\\ x=19.50\\\\ Lisa\ spent\ 19.50 \$\)
I think you just subtract the total - the money lisa spent
lets try it
25.50$-13.50$ = 12$
so we all know that its 12$
wanna PROVE IT , try adding 12$+13.50$ =
it will give us the total ;p