The correct options are
A 10
B 20
We know that sum of two sides is always greater than the third side.
AB + AC > BC,
since AC = 5 cm and AB = 15 cm
that means BC < 15 cm
Also, the difference between the lengths of any two sides of a triangle is always less than the third side.
AB - AC < BC,
since AC = 5 cm and AB = 15 cm
that means BC > 10 cm
∴ The side BC lies between 10 and 20.