This is not a finished answer. Only it's a way of showing how solve.
CIRCUMF. REV's in 6000 ft
REAR c+3 6000/(c+3)
FRONT c 6000/c
DIFFERENCE 100
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continuing....
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------------MAYBE try factorizations according to for 180.
3*60, 4*45, 5*36, 6*30, 9*20, 10*18, 12*15
That last one may work.
, .
Small wheel 12 feet;
Large wheel 15 feet.