9 identical cartons together weigh 72 kg. How many cartons of the same type would be needed to make up a total 168 kg?

The correct option is 21.

To find the total number of cartons needed to make up a weight of 168 kg, we can use the unitary method. First, we find the weight of one single carton.

We are given that 9 identical cartons weigh 72 kg.

Weight of 1 carton = $\frac{72}{9}$ = 8 kg.

Now, to find how many such cartons are needed to reach a total weight of 168 kg, we divide the total desired weight by the weight of a single carton:

Number of cartons = $\frac{168}{8}$ = 21.

Therefore, 21 cartons of the same type are required to make up a total weight of 168 kg.