Which two numbers (not digits) should be interchanged to make the given equation correct?

104 ÷ 8 – 15 + 4 × 26 = 21

104 ÷ 8 – 15 + 4 × 26 = 21

​$$\begin{array}{|c|c|} \hline\textbf{Operation preference wise} & \textbf{Symbol} \\\hline\text{Brackets} &[],{}, () \\ \hline \text{Orders, of} & (power), √ (root) , of \\ \hline \text{Division}& ÷ \\ \hline \text{Multiplication} & × \\ \hline \text{Addition} & + \\ \hline \text{Subtraction} & - \\\hline \end{array}$$​​

Option A: 15 and 4

Equation becomes:
104 ÷ 8 – 4 + 15 × 26 = 21

13 – 4 + 15 × 26 = 21

13 – 4 + 390 = 21

403  – 4 = 21

399 ≠ 21(Incorrect)

Option B: 8 and 26

Equation becomes:
104 ÷ 26 – 15 + 4 × 8 = 21 

4 – 15 + 4 × 8 = 21 

4 – 15 + 32 = 21 

36 – 15 = 21

21 = 21 (Correct)

Thus, correct option is (b).

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