Answer:
⁶/₃₅
Explanation:
If Redbeard takes 70 %, Whitebeard and Bluebeard must split the remaining 30 % (³/₁₀) of the treasure
If they split in a 4:3 ratio, Whitebeard gets ⁴/₇ of the 30 % and Bluebeard gets ³/₇.
Whitebeard's share is ⁴/₇(³/₁₀) = ²/₇(⅗) = ⁶/₃₅ of the total