Hey!
So when there is a scale factor you would always multiply it with the original dimensions, even if it wasn't a fraction.
so 4 time 1/5 is 0.8
and 6 times 1/5 is 1.2
so the dimensions of the model bed is 0.8 foot by 1.2 feet
Your answer is A!
Hope this helps!
In this question it basically wants you to leave Y alone in a side of the equation.
In this case,
For 3y=c

For Ay=w

For Y/c=w
Y=cw
For y/a=2c
y=2ac
For a=y+p
y=a-p
For C=y-k
y=C+k