The black rose carpet cheaper.
In this case the 4m wide is just enough (3.85 + 0.15 = 4) and you have to cut to the length of 2.35 + 0.15 = 2.50m. 2.5 * 4 = 10 m^2. The cost is 10 * 8 = £80.
In the second case you have to buy carpet with 4m length. After you bought it you have to cut the width to 2.50m. Hence you have to buy 3 * 4 = 12 m^2 carpet which costs 12 * 7 = £84
In conclusion the first choice is cheaper by £4.