Question 1157852
How?  Read your lessons.  First you learn about the Substitution Method.  Later you learn about Elimination Method.  


If you want substitution, then a couple or more ways to go but one of the easier may be:

6x+y=4
y=4-6x
substitute to 
x-4(4-6x)=19
x-16+24x=19
25x=19+16
x=35/25
x=7/5
and you should know what to do from here...