Answer: 12
Step-by-step explanation:
this is a right angled triangle so you use the pythagorean theory
which is a^2 + b^2 = c^2
you have c and b already. c is the hypotenuse.
a^2 + 16^2 = 20^2
a^2 + 256 = 400
a^2 = 400 - 256
a^2 = 144
then you square root 144 and get..
a = 12
