18) B

Number of slabs that can be bought with £140 = 140 ÷ 2.80 = 50 slabs

Dimensions of one slab = 70cm x 70cm = 0.7m x 0.7m

Area of 1 slab = 0.7m x 0.7m = 0.49 m²

Area that can be covered with 50 slabs = 50 x 0.49 = 50 x (49/100) = 49/2 = 24.5 m²

We know that the length covered is twice the width. Let the width be W. So length is 2W.

We can form the following equation:

2W x W = 24.5

2W² = 24.5

W² = 12.25

W = 3.5m

So we know the width covered by the slabs = 3.5m

Width of the whole patio= 5m

Width of flower garden = 5 – 3.5 = 1.5m