Am nevoie de ajutor la ex.42 si 43 va rog

42. a/2=b/12=c/25
8a+5b-3c=30
a=2k
b=12k }8×2k+5×12k-3×25k=30
c=25k 16k+60k-75k=30
76k-75k=30
1k=30 k=30
a=2×30=60
b=12×30=360
c=25×30=750
inca nu am facut invers proportionala