The base is 2 cm long and you want 3 pairs, that means 6 earrings.2 cm × 6 earrings = 12 cm
12 cm of the 50 cm have been used for the base.50 - 12 = 38 cm is left
An isosceles triangle has 2 sides that are isosceles and you want 6 earrings.2 sides × 6 earrings = 12 sides
To figure out the length for those 12 sides with the 38 cm wire that is left, you divide.38 cm ÷ 12 sides = approx 3.1 cm for each side