6x³+8x
First, replace all the x's with 5's since we're trying to find the value of this expression when x = 5.
6(5)³ + 8(5)
Solve for 5³, which is 5*5*5 = 125.
6(125)+8(5)
Do all the multiplication before addition (order of operations)
750 + 40
Now, add
790
That's your answer. Let me know if you need any clarifications.
Happy Studying~