How would i find the max/min of this function f(x) = 2x squared +18x +16

F(x)=2x²+18x+16
1) we have to calculate the first derived.

f´(x)=4x+18

2) Now, we equalize the first derived to "0" and find out the value of "x"
4x+18=0
4x=-18
x=-18/4=-4.5

3)we calculate the second derived
f´´(x)=4>0  ⇒we have a minimum at x=-4.5

4) Now we calculate the value of "y".
f(-4.5)=2(-4.5)²+18(-4.5)+16=40.5-81+16=-24.5

Therefore; Exist a minimum at (-4.5 , -24.5)

W-14=t. that i think is the answer idk