a)
well, she put 4000, and she earned in interest 960, so her accumulated amount is just their sum, 4960.
b)
now, it doesn't say, so we're assuming is <u>simple interest</u>, as opposed to compound interest.
c)
let's make the rate 1% greater then, and check
![\bf ~~~~~~ \textit{Simple Interest Earned} \\\\ I = Prt\qquad \begin{cases} I=\textit{interest earned}\dotfill\\ P=\textit{original amount deposited}\dotfill & \$4000\\ r=rate\to \stackrel{8+1}{9\%}\to \frac{9}{100}\dotfill&0.09\\ t=years\dotfill &3 \end{cases} \\\\\\ I=(4000)(0.09)(3)\implies I=1080 \\\\[-0.35em] ~\dotfill\\\\ \stackrel{\textit{at 9\%}}{1080}-\stackrel{\textit{at 8\%}}{960}\implies \stackrel{\textit{that much more}}{120}](https://tex.z-dn.net/?f=%5Cbf%20~~~~~~%20%5Ctextit%7BSimple%20Interest%20Earned%7D%20%5C%5C%5C%5C%20I%20%3D%20Prt%5Cqquad%20%5Cbegin%7Bcases%7D%20I%3D%5Ctextit%7Binterest%20earned%7D%5Cdotfill%5C%5C%20P%3D%5Ctextit%7Boriginal%20amount%20deposited%7D%5Cdotfill%20%26%20%5C%244000%5C%5C%20r%3Drate%5Cto%20%5Cstackrel%7B8%2B1%7D%7B9%5C%25%7D%5Cto%20%5Cfrac%7B9%7D%7B100%7D%5Cdotfill%260.09%5C%5C%20t%3Dyears%5Cdotfill%20%263%20%5Cend%7Bcases%7D%20%5C%5C%5C%5C%5C%5C%20I%3D%284000%29%280.09%29%283%29%5Cimplies%20I%3D1080%20%5C%5C%5C%5C%5B-0.35em%5D%20~%5Cdotfill%5C%5C%5C%5C%20%5Cstackrel%7B%5Ctextit%7Bat%209%5C%25%7D%7D%7B1080%7D-%5Cstackrel%7B%5Ctextit%7Bat%208%5C%25%7D%7D%7B960%7D%5Cimplies%20%5Cstackrel%7B%5Ctextit%7Bthat%20much%20more%7D%7D%7B120%7D)
