The equation of a line has the form:
[tex]y=mx+b[/tex]if the slope is equal to 4 then we know that: m = 4 and now we can replace the slope and the coordinate ( 2,1 ) to find b so:
[tex]\begin{gathered} 1=4(2)+b \\ 1-8=b \\ -7=b \end{gathered}[/tex]So the final equation will be:
[tex]y=4x-7[/tex]