Let's simplify the expression step by step:

Distribute the 4b:
4b(3b+6) = 12b^2 + 24b

Distribute the - and subtract the terms in the second parenthesis:
-(3b-5)(3b-5) = -9b^2 + 15b + 15b -25
= -9b^2 + 30b - 25

Combine the results:
12b^2 + 24b - (-9b^2 + 30b - 25)
= 12b^2 + 24b + 9b^2 - 30b + 25
= 21b^2 - 6b + 25

Therefore, 4b(3b+6) - (3b-5)(3b-5) simplifies to 21b^2 - 6b + 25.