Iwill give first answer brainliest.

a) +17 -9 = +8 . . . a profit of $8

b) +9 -5 = +4 . . . a rise of 4 cm

c) -6 -4 = -10 . . . a drop of 10 °C

Each integer has a sign chosen with respect to some reference direction. We usually choose a rise or increase or profit to be the positive direction, so a drop or decrease or loss is then represented by a negative number.

on friday there were 15 birds