Answer:
first one:
Area of a circle = π*r²
diameter (they gave) = 30ft
radius = diameter/2 = 15ft
π*15²= 706.85834705770347865409476123789
to nearest tenth= 706.9 ft
second question:
circumference = 2*π*r or d(diameter)*π
diameter = 30ft
30*π = circumference = 94.247779607693797153879301498385
in terms of π = 30π
Answer:

Explanation:
Build your conversion factors using the conversion table:
From the prefixes used in the metric system, you know that 1 deciliter = 0.100 liters. Then:
Arrange the expression to simplify the units and convert from cups to deciliters:
Round to the nearest tenth: 0.2 deciliter.
notice that the denominator can be factored into (x-3)(x+3).
Now you can cross out (x - 3) from the numerator and denomiantor resulting in a simplified fraction of 
Plug the limit value (which is 3) into the simplified fraction.
Answer: 
Move all the x terms to one side and solve for x. 15x-10x=21-6 : 5x/5=15/5 : x=3