bonsoir;

a)

3/5 = (3*7)/(5*7) = 21/35

b)

3/4 = (3/15)/(4*15) = 45/60

c)

80/100= (80/20)/(100/20) =4/5

d)

49/21 = (49/7) /(21/7) = 7/3