To determine the area of the floor in square yards, follow these steps:
1. Calculate the area of the floor in square feet:
- The length of the floor is 15 feet.
- The width of the floor is 21 feet.
- The area in square feet is found by multiplying the length by the width:
[tex]\[
\text{Area in square feet} = 15 \, \text{feet} \times 21 \, \text{feet} = 315 \, \text{square feet}
\][/tex]
2. Convert the area from square feet to square yards:
- There are 9 square feet in 1 square yard.
- To convert the area from square feet to square yards, divide the area in square feet by 9:
[tex]\[
\text{Area in square yards} = \frac{315 \, \text{square feet}}{9} = 35 \, \text{square yards}
\][/tex]
Therefore, the area of the floor in square yards is [tex]\( 35 \)[/tex]. The correct answer is [tex]\((C) 35\)[/tex].