Answer: 1875 seats since 1975.
Explanation:
Let's call the number of seats in the stadium after the first renovation S.
According to the problem, the number of seats was increased by 30% from the original 3000, so the number of seats after the first renovation was 3000 + (0.30 * 3000) = 3000 + 900 = 3900.
Now, the stadium's capacity is being increased by 25% from 3900, so the new number of seats is 3900 + (0.25 * 3900) = 3900 + 975 = 4875.
Finally, to find the total increase in seats since 1975, we subtract the original number of seats (3000) from the new number of seats (4875):
4875 - 3000 = 1875
Therefore, the guest capacity of McLean's baseball stadium has increased by 1875 seats since 1975.