Question 24970
First, assign values to Richard and John's marbles based on the wording of the problem.  We get:
x=John's marbles
4x=Richard's marbles


Next, write an equation based on the word clues in the probelm.  We get:
4x-18=x


Finally solve the equation.
4x-18=x
4x-x=18
3x=18
x=6
4x=24


The main problem with word problems is converting the words to a math problem that can be solved.  So, word problems are often primarily problems of interpretation.