Let x be the score that William needs to achieve.
Since there are 30 people in the class, there are 30 - 1 = <<30-1=29>>29 people without him.
Since their average was a 74%, this means that (29 * 74 + x) / 30 >= 75.
Thus, 29 * 74 + x >= 30 * 75
Thus, 29 * 74 + x >= 2250
Thus, 2146 + x >= 2250
Thus, x >= 2250 - 2146
Thus, x >= 94
#### 94