The expression (2 × 6) × 7 represents the number of times Julio went to the beach each week during 7 months. Which property is applied to write the equivalent expression 2 × (6 × 7) ? Please I just wish for an answer

The "i" in this problem actually doesn't represent imaginary numbers. This is a summation problem which is asking for the sum of (2i+1) for when i = 1 to i = 7.

So (2(1) + 1) + (2(2) + 1) + (2(3) + 1) + (2(4) + 1)... etc...

The summation rules we need to know for this problem are for constants and for a single variable.

When we have a constant, the summation rule is n*c where n is the number of times.

When we have a single variable, the summation rule is n(n+1)/2.

So applying the summation rules where n = 7:

2(7)(7+1)/2 + 1(7)

(7)(8) + 7 = 63

The answer to the summation is 63.