Alguien puede ayudarme con mi tarea de Formulas ? Can someone help me with my Formula Homeword ?

If you answer 2+2 you will get over 80 points

1. according to the internal revenue service, the mean tax refund for the year 2007 was $2,708. assume the standard deviation is $650 and that the amounts refunded follow a normal probability distribution. a. what percent of the refunds are more than $3,000? b. what percent of the refunds are more than $3,000 but less than $4,000? c. what percent of the refunds are less than $2,000?

Find the vertex for the parabola given by the function ƒ(x) = −3x2 − 6x.