je n'ai pas compris aidez moi svp

Exercice 1
1)
a) (-4,8) + (2.2) = -4.8-2.2 = -7
b) 25,7+(-33,7) = 25,7-33,7 = -8
c) (-141.1)+(-78.5) = -141.1-78.5 = -219.6
d) 45.5 +(-242.5) = 45.5 -242.5 = -197
e) (+5.8) + (+3.4) = 5.8 + 3.4 = 9.2
f) (-55.4)+33.2 = 33.2-55.4 = -22.2
g) 11.5 +(-81.2) = 11.5-81.2 = -69.7
h) (-58.7)+58.7 = 58.7-58.7 = 0

2) -219.6<-197<-69.7<-22.2<-8<-7<0<9.2

Exercice 3
La base d'un cylindre est un disque
aire de la base = PixR² = Pi x3² = 9Pi = 28,27 cm²

Volume d'un cylindre de révolution est aire de la base x hauteur :
Volume = 9Pi x 9
Volume = 81 pi
Volume = 254,47 cm cube