I think the question should have the Quantity 'A' asking for the ratio between QR/RS or QR/QT

In this case the Each rectangle inside the bigger rectangle has a width 'x'( Assume)

Now QR is nothing but the combination of 3 horizontally placed rectangles whose side length is the addition of the widths of those rectangles

QR = x+x+x = 3x ( From this ,the length of each of the rectangle is 3x - we can Conclude this by carefully noticing the 3 Horizontal rectangular widths = one vertically lying rectangular length)

Now coming to the denominator : If we need to Find out RS or QT we can notice the side is the combination of two rectangles which is Length of one Horizontal rect + width of vertical rect

So RS = x + 3x = 4x

Finally we get the ration as 3x/4x and we can cancel 'x' in numerator and denominator which is left with a ration of 3/4 and it is equal to quantity B

Question is asking about QS= ??

Thank you

Correct me in case of any mistakes