To cover the backyard they need 44700 square foot of sod.
Step-by-step explanation:
Area of the backyard = 250 x 180 ft
= 45000 square ft.
Area of the swimming pool = 15 x 20 ft.
= 300 square ft.
Area of the backyard available for planting sod = 45000 - 300
= 44700 square ft.
To cover the backyard they need 44700 square foot of sod.