a) A/B=4/5; A/C=3/2, so B=5A/4 and C=2A/3.
If A=1, then B=5/4, C=2/3.
A:B:C=1:(5/4):(2/3)
Multiply each ratio by the LCM of 3 and 4 (=12):
A:B:C=12:15:8.
b) B/C=(1/3)/(1/7)=7/3; A/B=(1/2)/(1/18)=9.
If B=1, C=3/7, A=9.
A:B:C=9:1:3/7.
Multiply each ratio by 7:
A:B:C=63:7:3.