three circles inscribed in a big circle

hello ! help me to solve this problem, please!!

its really hard for me ! thank you so much and God bless you richly !(Wink)

Three circles A,B and C are tangent externally to each other and each tangent internally to a larger circle having a radius of 10 cm. Radius of circle A is 5 cm.

a) compute the distance from the center of the larger circle to the point of tangency of the two circles B and C which are identical.

b) compute the radius of circles B and C.