Answer the next $6$ questions using the following marginal benefit $(MB)$ and marginal cost $(MC)$ functions for activity $A$ :

$MB=1600-5$A and $MC=900+9A$

and the following total benefit $($TB$)$ and total cost $($TC$)$ functions:

$TB=1600A-2\mathrm{.}5A^2$ and $TC=900A+4\mathrm{.}5A^2$

$1-$ Undertaking the ${35}^{th}$ unit of the activity A Net Benefit by

$2-$ Undertaking the ${75}^{th}$ unit of the activity A Net Benefit by

$3-$ The optimal level of activity $A^{**}$ is

$4-$ At the optimal activity level of $A^{**},$ Net Benefit is equal$-$to

$5-$ Eliminating the ${90}^{th}$ unit of the activity Total Benefit by and x Total Cost by

$6-$ What level of activity maximizes TOTAL Benefit?