Complete the following steps for the given function $f$ and interval.

a$.$ For the given value of n $,$ use sigma notation to write the left, right, and midpoint Riemann sums. Then evaluate each sum using a calculator.

b$.$ Based on the approximations found in part $($a$),$ estimate the area of the region bounded by the graph of f and the x $-$axis on the interval.

$f(x)=x^2-1on[2,5]$;$n=75$

a$.$ Write the left Riemann sum and evaluate. Select the correct choice below and fill in the answer box to complete your answer. $($Do not round until the final answer. Then round to two decimal places as needed.$)$

A$.{\displaystyle \underset{k=1}{\overset{75}{}}}((\frac{k49}{25}{)}^2-1)\frac{1}{50}=$

B$.{\displaystyle \underset{k=1}{\overset{75}{}}}((\frac{k49}{25}{)}^2-1)\frac{1}{25}=$

c$.{\displaystyle \underset{k=1}{\overset{75}{}}}((\frac{k50}{25}{)}^2-1)\frac{1}{50}=$

D$.{\displaystyle \underset{k=1}{\overset{75}{}}}((\frac{k50}{25}{)}^2-1)\frac{1}{25}=$