1)
y = 2x + 25.50
where x = the price of the first chair and y = the price of the second chair.
2)
y = 8x/3 OR y = 8/3 x (eight thirds times x)
3) y = 3x - 100
where x = the price of the other bed and y = the price of the "one bed"
If you don't understand one of them, just ask for an explanation.