Answer: 
Step-by-step explanation:
Area of Rectangle = bh = 16 ft x 18 ft = 288 
Area of Triangle = 1/2 bh = 1/2 x (16-12) ft x (6) ft x 2 (There's 2 triangles) = 24 
24 ft^2 + 288 ft^2 = 312 ft^2
£110 as 45mins times 4 radiators divided by 60 mins =3 hours
3 hours + 1 hour = 4 hours
4 hours times £20= £80
£80+£30=£110