Arun bought 5 bags of marbles, with each bag containing 4 marbles. A first person bought 30 marbles. How many marbles did they buy in total?

Based on the calculation shown, the first person bought 30 marbles.

$$\text{Marbles by first person} = 30$$

Arun bought 5 bags, and each bag contains 4 marbles.

$$\text{Marbles by Arun} = \text{Number of bags} \times \text{Marbles per bag}$$ $$= 5 \times 4$$ $$= 20$$

$$\text{Total marbles} = \text{Marbles by first person} + \text{Marbles by Arun}$$ $$= 30 + 20$$ $$= 50$$

The calculation shown in your work is correct.

The total number of marbles brought by both is $\text{50}$.