Line segment on is perpendicular to line segment ml. what is the length of chord ml?

OP = ON - PN, ON=Radius = 13 & PN = 8 (given) so OP 13-8 =5

Triangle MPO is a right triangle, then apply Pythagoras:

OM²  =  MP² + OP²===> 13²=MP² + 5²===>MP²=13² - 5² ==>MP²=144
& MP =√144 ==> MP =12
But a radius perpendicular to a chord bisects this cord in 2 equal part MP=24

ML is equal to 24 units

The discount is 8.70 . you dont tell us the percent of tax added so there is no way to find out, unless i'm not seeing anything. without tax its 37.70