If 1/5 can for 1 (each) room, then:
for 51 rooms, (51*1/5)=10.2 rooms.
Round to nearest whole number since you can't just paint 0.2 of a room: answer = 10
Answer:
The answer is the option 
Step-by-step explanation:
see the attached figure with letters to better understand the problem
we know that

-----> by vertical angles
-----> given problem
-----> given problem
substitute

This is all percentages so...
4/9 = 44%
2/7 = 29%
1/10 = 10%
Total = 83%
So 17% of 630 is left over which = 107
The triangle is equilateral
The answer is 173 ft²
The area of the patio (A) is half of the area of the circle (A1) with a diameter of 21 ft:
A = A1/2
The area of the circle with radius r is:
A1 = π * r²
π = 3.14
We do not have the radius, but we know that it is a half of the diameter:
r = 21 ft / 2 = 10.5 ft
A1 = 3.14 * (10.5)² = 346.18 ft²
So, the area of the patio is:
A = A1/2
A = 346.18 ft² / 2
A = 173.09 ft² ≈ 173 ft²