Introduction:
In this question, we are given the fraction 3/5 and we need to determine which of the given fractions is not equivalent to 3/5. We will analyze each option and compare it with 3/5 to find the correct answer.

Analysis:
Let's analyze each option one by one:

a) 768/1280:
To check if this fraction is equivalent to 3/5, we need to simplify both fractions to their simplest form.

- Simplifying 768/1280: Divide both the numerator and denominator by their greatest common divisor, which is 256.
768 ÷ 256 = 3
1280 ÷ 256 = 5

So, the simplified form of 768/1280 is 3/5. Therefore, this option is equivalent to 3/5.

b) 7509/12515:
Again, we need to simplify this fraction to check its equivalence with 3/5.

- Simplifying 7509/12515: Divide both the numerator and denominator by their greatest common divisor, which is 59.
7509 ÷ 59 = 127
12515 ÷ 59 = 211

So, the simplified form of 7509/12515 is 127/211. Therefore, this option is not equivalent to 3/5.

c) 369/625:
Let's simplify this fraction as well.

- Simplifying 369/625: Divide both the numerator and denominator by their greatest common divisor, which is 1.
369 ÷ 1 = 369
625 ÷ 1 = 625

So, the simplified form of 369/625 is 369/625. Therefore, this option is not equivalent to 3/5.

d) 513/855:
Once again, let's simplify this fraction.

- Simplifying 513/855: Divide both the numerator and denominator by their greatest common divisor, which is 171.
513 ÷ 171 = 3
855 ÷ 171 = 5

So, the simplified form of 513/855 is 3/5. Therefore, this option is equivalent to 3/5.

Conclusion:
After analyzing each option, we have found that option b) 7509/12515 is not equivalent to 3/5. The correct answer is b) 7509/12515.

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