Explanation:
a)
the total length of the outer or also only the inner perimeter ?
I assume the second case. but it is not difficult to change it to the outer perimeter case (per the information of b).
the total length consists of a straight side and 2 radius (left and right) of the end circles.
a radius is half the diameter, so 2×radius = 1 diameter.
so,
400 = length + 49
length = 400 - 49 = 351 m
the length of the straight sides is 351 m.
b)
the difference in length between both perimeters bases only on the difference in length of the circumference of the end circles. the lengths of the straight sides remain the same, not matter if outer or inner perimeter.
the circumference of 2 half circles is the circumference of 1 whole circle.
the circumference of a circle is
2×pi×r = pi×diameter
in our case for the inner perimeter
pi×49 = 153.93804... m
for the outer perimeter the radius and therefore the diameter changes : we have to add 6×1.5 m = 9 m on both sides of the circle
so, the radius of the outer circles is 9 m longer and the diameter 9×2 = 18 m longer : 49 + 18 = 67 m
so, we get for the outer circle perimeter
pi×67 = 210.4867078... m
therefore, the difference in the length of outer and inner perimeter is
210.4867078... - 153.93804... = 56.54866776... m