Four congruent ellipses are arranged as shown. What is the radius of the circle? Hint: First, show that if a line y=mx+b is tangent to an ellipse

my question is as follows:

four congruent ellipses are arranged as shown. what is the radius of the circle?

Four congruent ellipses are arranged as shown. What isthe radius of the circle? Hint: First, show that if a line y=mx+b is tangent toan ellipse (x/c)2 + (y/d)2 = 1, then it must satisfyb2 = 02m? + d2.