Statistics: how to do tcdf with an old calculator?

Polychlorinated biphenyl (PCB) is among a group of organic pollutants found in a variety of products, such as coolants, insulating materials, and lubricants in electrical equipment. Disposal of items containing less than 50 parts per million (ppm) PCB is generally not regulated. A certain kind of small capacitor contains PCB with a mean of 48.2 ppm and a standard deviation of 5 ppm. The Environmental Protection Agency takes a random sample of 40 of these small capacitors, planning to regulate the disposal of such capacitors if the sample mean amount of PCB is 48.5 ppm or more. Find the probability that the disposal of such capacitors will be regulated.
Here’s what I have so far:
Mean = 48.2
Std = 5
df = 40
T value = 48.5
48.5-48.2/[5/sqrt40]
= .3/[5/6.324555]
= .3/.790569
= .379474
Find P(t> 0.379474 when df = 40) = tcdf(0.379474,1000,40) = ?
My problem is that I only have an old “regular” calculator and don’t know how to do tcdf on it. A little help, please.

Use excel: =tinv(probability, df)