75% of 400 is 300. To calculate this, you can use the formula:

75/100 x 400 = 0.75 x 400 = 300

Alternatively, you can divide 400 by 4 to get 100, and then multiply by 3 to get 300:

400/4 = 100 100 x 3 = 300

Therefore, 75% of 400 is 300.