The length of QS is 27 units.
<u>Step-by-step explanation:</u>
In the given rectangle QRST QS and RT are the diagonals. In a triangle, the opposite sides are equal and parallel. This implies that the diagonals of a rectangle are equal.





We have obtained a quadratic equation here and solving this gives the possible values of QS.This can be solved using quadratic formula

The quadratic equation is of the form
here a=1 b=-2 c=-3


or

putting x=3 

putting x=-1

Since a length can have only positive values QS=27 units.
What is:
k/3 + 17 = 12?
k = -15
Add 1/4a to both sides
-4= 8/4a-3
Simplify
-4=2a-3
Add 3 to both sides
-1=2a
Divide both sides by 2
-1/2=a
Final answer: a=-1/2
Here's an answer it's number 2