Suppose that ${\displaystyle \underset{0}{\overset{1}{}}}f(t)dt=21.$ Calculate each $of$ the following.

$A.{\displaystyle \underset{0}{\overset{0\mathrm{.}5}{}}}f(2t)dt=$

$B.{\displaystyle \underset{0}{\overset{0\mathrm{.}25}{}}}f(1-4t)dt=$

$C.{\displaystyle \underset{1\mathrm{.}5}{\overset{2}{}}}f(4-2t)dt=$