[tex]\text{Look at the picture}[/tex]
[tex]\text{The slope:}\ m=\dfrac{\Delta y}{\Delta x}\\\\\Delta y=3,\ \Delta x=1\\\\m=\dfrac{3}{1}=3[/tex]
[tex]\text{The point-slope formula:}\ y-y_1=m(x-x_1)[/tex]
[tex](1,\ 5)\to x_1=1,\ y_1=5\\\\y-5=3(x-1)\to\boxed{Answer:\ 4.}[/tex]
