Which two numbers should be interchanged to make the given equation...

Given equation: (21 \times 4+(84 \div 7) \times 2-15 \times 5+42=105) Let's check each option one by one. Option 1) 4 and 2 Given: (21 \times 4+(84 \div 7) \times 2-15 \times 5+42=105) After interchanging the numbers we get; ($$\begin{aligned} & \rightarrow 21 \times 2+(84 \div 7) \times 4-15 \times 5+42=105 \\ & \rightarrow 42+12 \times 4-15 \times 5+42=105 \\ & \rightarrow 42+48-75+42=105 \\ & \rightarrow 132-75=105 \\ & \rightarrow 57 \neq 105 \end{aligned}$$) Option 2) 84 and 42 Given: (21 \times 4+(84 \div 7) \times 2-15 \times 5+42=105) After interchanging the numbers we get; ($$\begin{aligned} & \rightarrow 21 \times 4+(42 \div 7) \times 2-15 \times 5+84=105 \\ & \rightarrow 21 \times 4+6 \times 2-15 \times 5+84=105 \\ & \rightarrow 84+12-75+84=105 \\ & \rightarrow 180-75=105 \\ & \rightarrow \mathbf{1 0 5}=\mathbf{1 0 5} \end{aligned}$$) Option 3) 4 and 5 Given: (21 \times 4+(84 \div 7) \times 2-15 \times 5+42=105) After interchanging the numbers we get; ($$\begin{aligned} & \rightarrow 21 \times 5+(84 \div 7) \times 2-15 \times 4+42=105 \\ & \rightarrow \mathbf{2 1} \times 5+\mathbf{1 2} \times \mathbf{2}-\mathbf{1 5} \times \mathbf{4}+42=105 \\ & \rightarrow \mathbf{1 0 5}+\mathbf{2 4}-60+\mathbf{4 2}=105 \\ & \rightarrow 171-60=105 \\ & \rightarrow 111 \neq 105 \end{aligned}$$) Option 4) 7 and 21 Given: (21 \times 4+(84 \div 7) \times 2-15 \times 5+42=105) After interchanging the numbers we get; ($$\begin{aligned} & \rightarrow 7 \times 4+(84 \div 21) \times 2-15 \times 5+42=105 \\ & \rightarrow 7 \times 4+4 \times 2-15 \times 5+42=105 \\ & \rightarrow \mathbf{2 8 + 8}-75+42=105 \\ & \rightarrow 78-75=105 \\ & \rightarrow 3 \neq 105 \end{aligned}$$) Hence, the correct answer is "Option 2".