Calculate the sums for a$,$b$,$ and for c calculate the sum using the results from $($a$)$ and $($b$)$

$1\mathrm{.}8$ Evaluate the following sums:

a$.{\displaystyle \underset{i=0}{\overset{}{}}}\frac{1}{4^i}$

b$.{\displaystyle \underset{i=0}{\overset{}{}}}\frac{i}{4^4}$

c$.{\displaystyle \underset{i=0}{\overset{}{}}}\frac{i^2}{4^1}$