Answer:
A=4
Explanation:
you use the Pythagorean Theorem,
a triangle having a Leg b length of 3 and a Hypotenuse c length of 5 would have a Leg a length of 4.
Here is how I solved for Leg a using the Pythagorean Theorem.
Leg a = sqrt[ (Hypotenuse c)2 - (Leg b)2 ]
Leg a = sqrt[ (5)2 - (3)2 ]
Leg a = sqrt[ 25 - 9 ]
Leg a = sqrt[ 16 ]
Leg a = 4