book Maths Puzzle Numerical Ability

Hi, I'm trying to verify a graph that I did for a problem I've been working on. I am hoping that one of the tutors could please show me the solution to the below problem so I can

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Eve has two more marbles than Solene.
Solene has twice as many marbles as Steve.
Steve has 7 less marbles than Eve.
How many marbles do they have between them?</PRE>
3(x+1)=2x+7