Final answer:
The missing coefficient is -65.
Step-by-step explanation:
To find the missing coefficient, we need to expand the given expression and compare it with the given expression 25d² + cdotsd + 42.
Expanding (5d-7)(5d-6), we get 25d² - 35d - 30d + 42. Simplifying, we get 25d² - 65d + 42.
Comparing this with the given expression, we can see that the missing coefficient is -65.