Gọi x là số tấn hàng mà xe thứ ba chở được.

Theo đề bài, ta có hệ phương trình sau:
x + 4500 + 5400 = 3 * 600

Simplifying the equation, we get:
x + 9900 = 1800

Moving 9900 to the other side of the equation, we get:
x = 1800 - 9900

Simplifying the right side of the equation, we get:
x = -8100

Therefore, the third car can carry -8100 tons of goods.

However, since the weight of goods cannot be negative, we can conclude that the third car cannot carry any goods.