The formula

M$($t$)=1\mathrm{.}19$t $+13\mathrm{.}22$

gives the approximate total revenue, in billions of dollars, for McDonald's t years after $2000.$ The formula applies to the years $2000$ through $2013.$

$($a$)$

What is the value of

dMdt

$?$

$($Suggestion: Note that M is a linear function of t$.)$

dMdt

$=$