Solve the quadratic equation by completing the square

Me with this one question, and i'll upvote the brainliest answer

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

Given that abcd is a rhombus, what is the value of x?