Given, numbers are 15,18,35 and 42.
Then, the possible proportions are as follows:
15:18=35:42
15:18=1518=7×57×6=56
and
35:18=3518=7×57×6=56
∴ Ratio 15:18=Ratio 35:42
Hence, they form a proportion.
15:35=18:42
15:35=1535=3×57×5=37,
and
18:42=1842=6×67×6=37
∴ Ratio15:35=Ratio18:42
Hence, they form a proportion .
42:18=35:15
42:18=4218=7×63×6=73,
and
35:15=3515=7×53×5=73
∴ Ratio 42:18=Ratio 35:15
Hence, they form a proportion .
42:35=18:15
42:35=4235=7×67×5=65,
and
18:15=1815=3×63×5=65
∴ Ratio 42:35=Ratio 18:15
Hence, they form a proportion .