Do u know how to do i just need #31

Which is an equation for the nth terms of the sequence 12,15,18,21

For how answer my question this will be the last question can you answer in math subject

Since opening night, attendance at play a has increased steadily, while attendance at play b first rose and then fell. equations modeling the daily attendance y at each play are shown below, where x is the number of days since opening night. on what day(s) was the attendance the same at both plays? what was the attendance? play a: y = 8x + 191 play b: y = -x^2 + 26x + 126