Resposta :
Olá,
[tex] \tt \: 35 + [ -21 - ( - 12 + 15 )] \\ \tt \: 35 + [ -21 - ( 3 )] \\ \tt \: 35 + [ -21 - 3] \\ \tt \: 35 + [ -24] \\ \tt \: 35 - 24 \\ \tt \: 11 \\ [/tex]
Portanto:
[tex] \boxed{ \tt \: a) \: + 11} \: \checkmark \\ [/tex]
Olá,
[tex] \tt \: 35 + [ -21 - ( - 12 + 15 )] \\ \tt \: 35 + [ -21 - ( 3 )] \\ \tt \: 35 + [ -21 - 3] \\ \tt \: 35 + [ -24] \\ \tt \: 35 - 24 \\ \tt \: 11 \\ [/tex]
Portanto:
[tex] \boxed{ \tt \: a) \: + 11} \: \checkmark \\ [/tex]