a) $(-12)+83+(-48)+17$
=$( -12 - 48 ) + ( 83 + 17 )$
= $( - 60 ) + 100$
= $40$
b) $12+(-24)-2+24$
= $( 12 - 2 ) + ( -24 + 24 )$
=$10 + 0 =10$
c) $48.69+31.48$
= $48 ( 69 + 31 )$
= $448 . 100 = 4800$
d) $18 : 3² + 5 . 2³$
= $18 : 9 + 5 . 8$
= $2 + 40 = 42$