The easiest literal equations to understand are formulas where one variable is expressed in terms of the others. To solve for a given variable, isolate that variable on one side of the equation so that it's solved in terms of the other variables. Make sure to use the same operations on both sides of the equation!
Let x be the unknown quantity. You have,
x/10+11=3*x/5
Then,
x=22 galons are in the container
