Can someone answer these questions for me please​

Which equation results from adding the equations in this system? x+6y=9 and -x+2y=-15

Nikolas calculated the volume of the prism. his work is shown below.

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?