You need to know that:
1 ounce = 28.35 grams
So, 1 tube contains
3.0 oz × 28.35 = 85.05g total mass
Mass of Benzyl salicylate =
2.40/100 = Percentage of Benzyl salicylate (in numerical value)
= 0.024
0.024 × 84 = Mass of Benzyl Salicylate
=2.016g
If one tube contains
2.016g × 425 tubes
=856.8g
Then,
Converting into kg by (dividing by 1000)
=856.8 ÷ 1000
= 0.8568 grams
= 0.857g (3sf)