find area of triangle whose perimeter is 180 & two of its sides are 18 & 80 cm. also calculate the altitude of the triangle corresponding to the shortest side .

perimeter = a + b + c 
180 = 18 + 80 + c
180 - 98 = c
82 cm = c
hence, s = a + b + c / 2
s = 90 cm
area by heron's formula = root s(s - a)(s - b)(s - c)
= root 90 *10*8*72
=720 cm²
hence, area = 1/2 * b*h
720 = 1/2 * 82 * h
720 = 41 * h
720 / 41 = h
17.56 cm²