Mark is shopping to replace his bicycle's wheels. He places two wheels, one with a radius of 60 centimeters and one
with a radius of 40 centimeters, parallel with each other as if
they were the two front tires of a car on level ground. As he
does so, he notices that in the late afternoon light their shad-
ows end in the same below, as shown in the diagram below.
How far apart did he place the wheels, measuring from the
wheel's left edges? (Note: the wheels' widths are negligent.)
wheel 1
wheel 2
60 cm
40 cm
d
75 cm