(2b - 5)(2b + 5) =?

Please help! Polynomials are difficult for me..

Can someone answer this question for me

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 the value for this expression? 2e-5