Question 398
If {{{y=x+4}}} and {{{y=3x}}} then substituting the second equation into the first gives us:

{{{3x=x+4}}}

This is now simple to solve for x:

{{{2x=4}}}
{{{x=2}}}

We can now substitute this value into either of the first equations to get the value of y (I'll use the first):

{{{y=2+4}}}
{{{y=6}}}

Result:
{{{x=2}}}, {{{y=6}}}. Graphically, this means that the 2 lines intersect at (2,6), as can be seen if we put them onto a graph:

{{{graph(300,200,-3,6,-1,8,y=x+4,y=3x)}}}