Question 1034035
There are two ways we can do this.  We can either solve it using substitution or elimination.  I will do both.<br>

Solving using Substitution:
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To solve the system using substitution we need to solve one of the equations for y.  Since the second equation has y with no number(coefficant) in front of it we can solve that equation for y easily.  <br>
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3x - y = 4 Subtract 3x from both sides
-y = 4-3x  Divide by -1
y = -4+3x<br>
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Now that we have an expression for y we can substitute(hence the name of the method) that into the first equation and solve for x.  <br>
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6x + 3y = 13 Substitute 4+3x in for y
6x + 3(-4+3x) = 13 Distribute the 3
6x - 12 + 9x = 13 Combine Like terms
15x - 12 = 13 Add 12 to both sides
15x = 25 Divide both sides by 15
x = 25/15 Simplify the fraction
x = 5/3<br>
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Solving using Elimination:
To solve the system using elimination we need to eliminate a varable.  Since your question specifically asks what the value of x is we should eliminate y.  To do this we multiply both sides of the bottom equation by 3 and add the two equations together.  <br>

3(3x - y) = 3(4) Distribute
9x-3y = 3(4) Multiply on the right
9x-3y = 12<br>

Adding our equations together we get
6x+3y=13
9x-3y=12
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15x = 25<br>

Now we can solve the equation for x by dividing both sides by 15.  Simplifying our answer we get the same 5/3 we got above.