HELP !! Its A Math Problem

Arefrigeration system at your company uses temperature sensors fixed to read celsius (°c) values, but the system operators in your control room understand only the fahrenheit scale. you have been asked to make a fahrenheit (°f) label for the high temperature alarm, which is set to ring whenever the system temperature rises above –10°c. what fahrenheit value should you write on the label

What is always true when two whole numbers are subtracted?

According to the general equation for conditional probability if p(anb)=3/7 and p(b)=7/8 what is p(a i b)