Suppose parametric equations for the line segment between $(4,8)$ and $(2,-9)$ have the form:

$x=a+bt$

$y=c+dt$

If the parametric curve starts at $(4,8)$ when $t=0$ and ends at $(2,-9)$ at $t=1,$ then find $a,b,c$ and $d.$

$a=$

$b=$

$c=$

$d=$