Let me repeat (and correct) what I've said in my comment ad reply to your edit.

You have to transfer from $X$ to $Z$ in order to use a z-score table. Since a z-score table contains a small finite subset of values, you often must settle for an approximation. So you could also settle for $P(Z<-3)\approx 0$ and $P(Z< 3)\approx 1$ (NB: $P(Z>3)\approx 1$ was a typo, sorry.)

As to $P(-1.25<Z<3.75)$, I'll use [this z-score table](http://www.regentsprep.org/Regents/math/algtrig/ATS7/ZChart.htm):
$$P(-1.25<Z<3.75)=P(Z<3.75)-P(Z<-1.25)\approx 1-0.1056=0.8944$$