Jerry started doing sit-ups every day. The first day he did 19 sit-ups. Every day after that he did 4 more sit- ups than he had done the previous day. Today Jerry did 81 sit-ups. Write an equation that could be solved
to find the number of days Jerry has been doing sit-ups, not counting the first day. Let n represent the
number of days.
An equation that can help Jerry to find the number of days he has been dolng sit-ups is given by

81 - 19 = 62 ÷ 4 = 15.5 days (?)

for the friend request.

when a figure, such as triangle (xyz) is reflected over the line y = x to create x'y'z' the x-coordinates and y-coordinates of the original image (pre-image) will be reversed for the image. (e.g., (x, y) > (y, x)) this means that the pre-image position of the x- and y-coordinates switch places which in turn provides a mirror like image of the original xyz.  

i notice that when i draw a line segment from x to x', that the points are parallel from each other -- they are exactly across from each other and do not intersect with any other points.  

yes, think i would see the same characteristic if you drew the line segment connecting y with the reflecting line and then y' with the reflecting line because of the essence of reflections. because it is a mirror image, each point was effected the same way which leads me to conclude that they same would apply to y and y'.