It cost $8,428.80
The first step to solving this problem is to find the area of the deck in square yards. We can do this by multiplying the length by the width:
Area of the deck = Length x Width = 8 yards x 12 yards = 96 square yards
Next, we can find the total cost of building the deck by multiplying the area by the cost per square yard:
Total cost = Area of the deck x Cost per square yard
Total cost = 96 square yards x $87.85 per square yard
Total cost = $8,428.80
Therefore, it cost $8,428.80 to build Ryan's backyard deck.