Which two numbers (not individual digits) should be interchanged to make the given equation correct?$3\times 9\times 7–18\times 4+(72÷8)–21=186$

Let's test the options by interchanging the numbers to see which one balances the equation to 186.Test Option B (interchanging 3 and 4):The equation becomes:
$$4\times 9\times 7-18\times 3+(72÷8)-21$$
Let's compute using BODMAS:Parentheses: $72÷8=9$ Multiplications:$4\times 9\times 7=36\times 7=252$$18\times 3=54$ Substitute back into the expression:
$$252-54+9-21$$
Addition/Subtraction from left to right:$252-54=198$$198+9=207$$207-21=186$ Since $186=186$, Option B correctly satisfies the condition.