The way to work it out and the value of the value of the equation

17 is your sender because 3+1= 4 and divide by 12 is 3 + 6 = 9 and times it by 2 and subtract by 1 = 17

2 × {6 + [12 ÷ (3 + 1)]} - 1

for this expression, you need to start with the innermost parentheses and work your way out--do (3 + 1) FIRST, then worry about what's inside the [square brackets].

2 × {6 + [12 ÷ (4)]} - 1 ... now divide 12 by 4
2 × {6 + [3]} - 1 ... now add 6 and 3
2 × {9} - 1

now follow the order of operations, PEMDAS. multiply first, then subtraction second:

2 × 9 - 1 ... multiply 2 and 9
18 - 1 ... subtract
17 is your result.