For lines to be parallels the slopes must be equal, for the lines to be perpendicular the lines have to be inverse reciprocals meaning if you have a slope of 1/2X then the perpendicular line must be -2X
The cost of the monthly fee is 50$.. if the joining fee is 100.. take 200 and subtract that fee since it is included in the total. You’re left with 100. Note, the 200 is calculated for a 2 month period, so split the remaining 100 ,from the total 200, into 2. You’re left with 50 each month.
T=(C-100)/2 (T being 1 month) (C being the total cost/200)
