What is the derivatives

If h and k are functions of x, then the derivative of hk is what?
Selection for answers:
hk+h'k'
hh'-kk'
h'k-hk'
k'h+kh'
Please explain what you did to get the answer. I am so confused. Thanks!

let's do something simple to show you the product rule

let h=x+1 and k=x+3
then h*k = (x+1)(x+3)=x^2+4x+3
the derivative is 2x+4

now the product rule says that if you have
if you want the derivative of two functions multiplied together then you do this
f '(hk) = h' * k + h * k'
let's see if we get the same answer
h' = 1, k=(x+3), h=(x+1), k' = 1
1*(x+3) + (x+1)*1= 2x+4
they are the same.
dnadan1

Product rule
k'h+kh'