Answer :

If u substitute in the values, c=5 and d=4 into the expression, u get
6(5)^2-5(4)+8
=6(25)-20+8
=150-20+8
=130+8
=138
sydneyhenderson
Well okay first you want to write the expression.

6c²-5d+8 (next you replace the c with 5 and d with 4)

6(5)²-5(4)+8  (now you want to go left to right, first you want to do 5²)
6(25)-5(4)+8   (like always left to right :D  ** 6 × 25**)
150-5(4)+8     (5 × 4, then 150· 5×4 )
150-20+8
130+8   (Now you add :D )
138 

Final answer is 138 

I hope I helped you out! :D