Question 1144740
.
<pre>

From the condition,  {{{3/7}}}  marbles are blue.


Hence,  {{{3/7}}} of the marbles are 18 blue marbles.


It means, that  {{{1/7}}} of the marbles is  {{{18/3}}} = 6 marbles.


Therefore, the number of the blue marbles is 6*7 = 42.


Altogether, Ben has 18 + 42 = 60 marbles.    <U>ANSWER</U>
</pre>


Solved MENTALLY, without using equations.