we know that
one revolution is equal to the circumference of a circle
circumference C=pi*D
where
D is the diameter of a circle
step 1
divide 136 ft by 20 revolutions
so
136/20=6.8 ft
that means one revolution is 6.8 ft
C=6.8 ft
C=pi*D
pi*D=6.8------> divide by pi both sides----> D=6.8/pi
D=6.8/3.14-------> D=2.166 ft
convert to in
1 ft---------> 12 in
2.166 ft----> x
x=2.166*12----> x=25.98 in-------> 26 in
the answer is
The diameter is 26 in