Question 1863
from memory i think it is -40 degrees, so lets see...

where the 2 scales are the same... so lets re-write f as c. We then get

{{{C = (5(C-32))/9}}}
{{{9C = 5(C-32)}}}
{{{9C = 5C - 160}}}
{{{4C = -160}}}
{{{C = -40}}}

there you go.

cheers
Jon.