Question 326508
Re-read your setup.
N - words per minute (wpm)
t - weeks
Here's how to solve.
{{{N(t)=157/(1+5.3e^(-0.12t))}}}
{{{50=157/(1+5.3e^(-0.12t))}}}
{{{1+5.3e^(-.12t)=157/50=3.14}}}
{{{5.3e^(-0.12t)=2.14}}}
{{{e^(-0.12t)=0.403776}}}
{{{-0.12t=ln(0.403776)}}}
{{{-0.12t=-0.9069}}}
{{{t=7.56}}} 
A little over seven and a half weeks.
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Now follow the same steps and solve for t when N=75.