Bonjour,

a. 2/7 + 4/9

= (2 x 9)/(7 x 9) + (4 x 7)/(9 x 7)

= 18/63 + 28/63

= 46/63

b. 3/8 - 5/3

= (3 x 3)/(8 x 3) - (5 x 8)/(3 x 8)

= 9/24 - 40/24

= -31/24

c. -4/5 - 7/9

= (-4 x 9)/(5 x 9) - (7 x 5)/(9 x 5)

= -36/45 - 35/45

= -71/45

d. 1 + 2/9

= 1/1 + 2/9

= (1 x 9)/(1 x 9) + 2/9

= 9/9 + 2/9

= 11/9

e. 1 - 7/3

= 1/1 - 7/3

= 3/3 - 7/3

= -4/3

f. 3 + 3/4

= 3/1 + 3/4
= (3 x 4)/(1 x 4) + 3/4

= 12/4 + 3/4

= 15/4