Răspuns :
5A+21-(13-1):2=7
5a+21-12:2=7
5a+21-6=7
5a+15=7
5a=7-15
5a=8
a=8/5
5a+21-12:2=7
5a+21-6=7
5a+15=7
5a=7-15
5a=8
a=8/5
5a+21-[(6+7)-1]:2=7
5a+21-(13-1)=7x2
5a+21-12=14
5a+21=14+12
5a+21=26
5a=26-21
5a=5
a=5:5
a=1
5a+21-(13-1)=7x2
5a+21-12=14
5a+21=14+12
5a+21=26
5a=26-21
5a=5
a=5:5
a=1