Answer:
The length of the longest side is 68mm
Step-by-step explanation:
The perimeter of a triangle is equals to the sum of all its sides
P=a+b+c
The triangle is isosceles, so two of its sides are equal, have the same length.
So: a=b, then
P=2a+c=168mm
Moreover, we know that the base is 18mm more than each of the legs, this means: c=18mm+a, where we obtain that a=c-18mm.
So, the system of equations is solved, lets use the above result in Perimeter`s equation.
168mm=2*(c-18mm)+C
From here we have:
168mm=3c-36mm
We obtain the following result: c= 68mm, this the length of the longest side
