Those results are correct.
39, 45, 75
The middle number is 45, this is the median.
30, 75, 180, 1740
The middle numbers are 75 & 180. Exactly half way between these numbers (180 - 75 = 105, which is the difference between the numbers. 105/2 = 52.5, which is half the difference. 75+52.5 to put the lower boundery back makes it 127.5) is the median.