At 7am last night, the temperature was 10°f. at 7am the next morning, the temperature was -2°f. by how much did the temperature change from 7pm to 7am?

The temperature dropped 1 degree an hour

Use the Pythagorean theorem. The equation for this right triangle would be a^2+b^2=c^2. Since you have one leg and the hypotenuse, you can plug these into the equation. It would be 7^2+b^2=12^2. Do the exponents. You will get 49+b^2=144. You need to get b by itself so subtract each side by 49. You get the equation b^2=95. Square root each side to get b=9.746. This rounds to 9.7. So the answer is A. Hope this helps! ;)