Answer
$y=2.1x+49.4$
Work Step by Step
$(4, 57.4)$ and $(5, 59.5)$
$m$ = change in y/change in x
$m = (59.5-57.4)/(5-4)$
$m = 2.1/1$
$m=2.1$
$y=mx+b$
$57.4=4*2+b$
$57.4=8+b$
$57.4-8=8+b-8$
$49.4 =b$
$m$ says how a change in $x$ is affected, and $b$ shows at what value $y$ starts.