7.5x10^14 - 3x10^16

To subtract these numbers, we need to make sure both numbers have the same exponent.

7.5 × 10^14 can be written as 75 × 10^13 (since 7.5 = 75 × 0.1)

Now we can subtract:

75 × 10^13 - 3 × 10^16

Since the exponent in the second number is larger, we can't directly subtract them. We need to adjust the first number to also have an exponent of 16, by multiplying by 10^3:

75 × 10^13 × 10^3 = 75 × 10^16

Now we have:

75 × 10^16 - 3 × 10^16

We can now subtract the two numbers:

75 - 3 = 72

So the final result is:

72 × 10^16