How can I find the length of bisector in triangle ,if I have all sides​

How to use order of operation in 20 divide by 4 multiply 5 = 1

Aretha wanted to gather data about the cost of local bowling leagues in her area. she plotted the data and determined that the average bowling league costs consist of a one-time registration fee and a monthly fee modeled by the equation y = 15x + 20. identify and interpret the y-intercept in this model. the y-intercept is 20. this is the cost per month. the y-intercept is 20. this is the cost of registration. the y-intercept is 15. this is the cost of registration. the y-intercept is 15. this is the cost per month.

What is the common difference for this arithmetic sequence? -6,-2,2,6,10 a.4 b.5 c.3 d.6