The time t in hours, employees are on the working on assembling widgets. The employee rate of change of productivity in units per hour is described by

r(t)=139(t2+7t)t3+7t+15,0t8\displaystyle {r}{\left({t}\right)}=\frac{{{139}{\left({t}^{{2}}+{7}{t}\right)}}}{{{t}^{{3}}+{7}{t}+{15}}},{0}\le{t}\le{8}

limt2r(t)=\displaystyle \lim_{{{t}\rightarrow{2}}}{r}{\left({t}\right)}= units per hour

If needed round to 4 decimal places