15-3=12, so Monique spent $12 on Squid. So now set the problem up as 6x=12 where x is 1 pound of squid, 6 is how many pounds she bought, and 12 is the price for 6 pounds. Solve...
6x=12 Divide by six on each side to get x=2, so...
The cost of one pound of squid is $2.
Hope this helps!
P.S. the full equation is 6x=15-3, but I wrote it as 12 because we already subtracted the 3 at the beginning.
