Write these numbers in standard form: a)200,000 b)80,000 c)900,000,000 d)1,000,000,000

What is the missing step in this proof ?

How many solutions does the nonlinear system of equations graphed bellow have?

Sanya noticed that the temperature was falling at a steady rate of 1.4 degrees every hour from the time that she first checked her outdoor thermometer. by 6 a.m., the temperature had fallen 21 degrees. which expression can you use to find how many hours earlier she had first checked the thermometer?