$\begin{array}{l}\text{Here, }\\ \Rightarrow \text{56\% of 450 + ? = 300}\\ \\ \text{It can be simplified as}\\ \\ \Rightarrow \frac{56}{100}\times 450+?=300\\ \\ \Rightarrow \text{56}\times \text{4.50 + ? = 300}\\ \\ \Rightarrow \text{252 + ? = 300}\\ \\ \Rightarrow \text{? = 300}-\text{252 = 48}\end{array}$

Hence, option B is correct.