95% C.I. = mean + or - 1.96(standard deviation / sqrt(sample size))
95% C.I. = 57 + or - 1.96(3.5/sqrt(40) = 57 + or - 1.085 = 57 - 1.085 to 57 + 1.085 = 55.92 to 58.09
Therefore, 95% of the mean will occur in the interval 55.92 to 58.09
The perimeter of the triangle is : 12.6.
This result is obtain by the use of triangle perimeter formula :

Where : a is the distance between the points A and B
b is the distance between the points B and C
c is the distance between the points C and A