Question 895033

A certain  process requires that room temperature be lowered from 40 degrees Celsius at the rate of 5 degrees Celsius every hour.What will be the temperature temperature 10 hours after the process begins. I know it's about integers, and the answer is -10° Celsius, but I need the solution on how to find the answer.
<pre>
Lowering it {{{5^o}}}C every hour for 10 hours results in total lowering of 5(10), or {{{50^o}}}C. 
Lowering the temperature, {{{50^o}}}C, from {{{40^o}}}C means that the temperature, after a 10-hour period is:
{{{40^o - 50^o}}}, or {{{highlight_green(highlight_green(- 10^o))}}}C