The diameter is 30 cm, therefore the radius is 15 cm. The circumference of the tire is found by using the formula C = 2πr. C ≈ 2(3.14)(15) ≈ 94.2 cm. 5 km = 500,000 cm (5 x 1000 x 100). 500,000 ÷ 94.2 ≈ 5307.86 or about 5300 times (revolutions). (using π, instead of 3.14, I got 5305.16 revolutions)