Rauhan

If it is then I will explain how I got it.

I am not 100% sure if this answer is correct but is the answer $\frac{7}{6}$

@CPhill can we just find the midpoint and divide the answer by 4??

I wish I could help u guys but I forgot how to solve these type of questions cuz I used to solve them in grade 9 and 10

So the coordinates of A and B are basically finding the mid-point of RS and ST.

1^st  to find the mid-point u use the formula $(\frac{x_1+x_2}{2}, \frac{y_1+y_2}{2})$

The mid-point of RS is,

$(\frac{0+2a}{2}, \frac{0+2b}{2})$ 

$(\frac{2a}{2}, \frac{2b}{2})$

$(a,b)$

$(a,b)$ are the coordinates of A.

Now the midpoint of ST is,

$(\frac{2a+2c}{2}, \frac{2b+2d}{2})$

$(\frac{2(a+c)}{2}, \frac{2(b+d)}{2})$

$((a+c),(b+d))$

$((a+c)+(b+d))$ are the coordinates of ST.

I didn't quite understand what the slope part means

Finally, after a very long time, my answer was chosen as the best answer; worked so hard for this

So the formula for finding the midpoint is 

$(\frac{x_1+x_2}{2}, \frac{y_1+y_2}{2})$

Substituting the values gives

$(\frac{-1+3}{2}, \frac{9+8}{2})$

$(1,\frac{17}{2})$

$(1,8.5)$

I understood that

I dont use mac but in the later question related to this chapter( if any) i will still try the command

Thanks for briefly explaining this question cuz i was still a bit lost on this one even after Hectictar explained it