Step-by-step explanation:

For quite some time now, calculators have had statistical functions built in. Here we need to use the stat. function normalcdf, which has only two inputs when we're working with z scores instead of raw scores.
Here,
normalcdf(-100,1.25) = 0.894
This same result could be obtained using a table of z-scores.
You mean to simplify as this is an expression not an equation, as it has no equal sign...
Factor our 4 first
(4r^3t^2)/(-rt)
Now factor out -rt
-4r^2t