a. ( +5 ) + ( +3) = ( +8 )

b. ( +7 ) + ( -5 ) = ( +2 )

c. ( -13 ) + ( +5 ) = ( -8 )

d. ( -5 ) + ( -7 ) = ( -12 )

e. ( +4 ) + ( -7 ) = ( -3 )

f. ( -4 ) + ( +12 ) = ( +8 )