Answer: 3.1 cm
Explanation:isosollese triangle has 2 equal sides that are longer than legnth of base
perimiter=15.7
equation is 2a+b=15.7
so if the longer side is 6.3, wat is legnth of base
we know that identical sides are bigger so 6.3 is one of the identical sides
2a means the 2 idneical sides
2(6.3)+b=15.7
12.6+b=15.7
subtract 12.6 from btohs ides
b=3.1
answer is base=3.1 cm