Question

efectuar 28-[21-(12-3)/3]-7]

Answer 1

$28 - (21 - ( \frac{12 - 3}{3} ) - 7) \\ 28 - (21 - \frac{9}{3} ) - 7 \\ 28 - (21 - 3) - 7 \\ 28 - 18 - 7 \\ 3$

Answer 2

28-[21-((12-3)/3)]-7]
28-[21-((9)/3)]-7
28-[21-3]-7
28-[18]-7
10-7
3