A cell phone plan costs ​$29.80 per month for 800 minutes of talk time. It costs an additional ​$0.07 per minute for each minute over 800 minutes. To get​ e-mail access, it costs 20​% of the price for 800 minutes of talk time. Your​ bill, which includes​ e-mail, is the same each month for 8 months. The total cost for all 8 months is ​$320.80. Write and solve an equation to find the number of minutes of talk time you use each month.

2x^2+5x+17

your welcome. : )

the solution of the equation is 2.23 ⇒ answer b

step-by-step explanation:

* lets revise the meaning of exponential function

- the form of the exponential function is y = ab^x, where a ≠ 0, b > 0 ,  

  b ≠ 1, and x is any real number

- it has a constant base b

- it has a variable exponent x

- to solve an exponential equation, take the log or ln of both sides,  

  and solve for the variable

* lets solve the problem

∵

- the base is 7 and the exponent is x

- insert ㏑ in both sides

∴

- use the rule

∴ x ㏑(7) = ㏑(77)

- to find x divide both sides by ㏑(7)

∴

* the solution of the equation is 2.23 to the nearest 2 decimal places