Answer:
When we have a statement:
If P then Q
Where:
P is the hypothesis.
Q is the conclusion
The Law of Detachment says that:
Statement 1: if P, then Q.
Statement 2: P is true:
the law says that: Q is true.
In this case:
Statement 1: "If A is less than 90°, then A is an acute angle."
P = A is less than 90°
Q = A is an acute angle
Statement 2: A = 75°.
Then by statement 2 we know that A is smaller than 90°.
Then P is true.
This means that, by the Law of Detachment, Q is also true.
Then we can conclude that A is an acute angle.