There is a typing mistake in the data for the perimeter, it appears. Also the triangle is perhaps an isosceles triangle ... It is difficult to understand the question, when some data is not good.
the perimeter is probably = 40 1/2 cm or 401/2 cm.
the base = 34 cm.
so, the length of the other two sides : (perimeter - base ) /2
= 3.25 cm or 83.25 cm