We are told that 240 is 2/5 of the total cost of the trip. We can picture this situation as follows
THe whole bar represents the total cost of the trip. If we split it in 5, the two coloured tiles represent 2/5 of the total cost. We are told that these two tiles represent 240. Let x be the total cost of the trip. One tile of the picture would be

We have two tiles, so that would be

NOw, we know that two tiles represent 240. So we have the following equation

Now, we simply need to find the value of x. To do so, we first multiply by 5 on both sides. Then we get

Now, we divided both sides by 2. So we get

Then, the total cost of the trip is 600.