Performing If Statement in Python Parser of ArcGIS Field Calculator?

Question

I've one field "MAXSPEED". I want a Field Calculation that will calculate an additional field ("noise"):

If MAXSPEED> 40 then the term: (73.5 + Log ( 25 ) * ( [MAXSPEED] / 50)) should be used to calculate "noise" but if MAXSPEED < 40 then "noise" should be 71,1

I have no programming experiences. Python or VB, both works for me.

Edit: sl = maxspeed

I figured out the term wasn't alright. This is the right one 73.5 + 25log(sl/50)

import math
def test(sl):
 if sl>=40:
 result = 73.5 + (25*(math.log(sl/50.0))
 elif 30<=sl<40:
 result = 71.1
 else:
 result = 0
 return result

The result for sl = 50 is alright (73.5) but all values>50 are wrong:
sl(60) = 78.06 instead of 75.47
sl(70) = 81,91 instead of 77.15

Answer 1

in the field calculator, with Python parser, check for "codeblock" and enter

import math
def test(maxspeed):
 if maxspeed >= 40:
 return 73.5 + math.log10(25) * (maxspeed/50)
 else:
 return 71.1 

then enter NOISE =

test(!MAXSPEED!)