Hello, midnightnurse!

We need more information.

A full description of the figure is required.

Presently, I amthe following "facts" . . .guessing

We have a quadrant of a circle with radius 4 (the "4-circle").

There is a semicircle of radius 2 (the "2-circle").

The "4 cm" at the bottom isthe length of the chord.not

. . It is obviously a radius of the 4-circle.

We have a mystery circle tangent to the 2-circle.

It appears to extendthe 4-circle.beyond

With no further constraints, it could haveradius.any