Need asap question is in the picture show work plz

Synthetic division is the easiest to try and explain in this forum. If x - 5 is a factor of that polynomial, when you divide you will get a 0 remainder.  If x - 5 = 0, then x = 5.  That will be the number we put inside the little box using synthetic division. 5∫       3       0       0       -4
                                       15__125___625     That's the synthetic division.
                                       3        15    125     621
Hopefully it retains it formatting.  Bring down the first 3 and multiply it by 5 to get 15 and put that 15 up under the first 0 (place holder for the missing x^2 term).  Add 0 + 15 to get 15.  Multiply 5 by 15 to get 125.  Put the 125 up under the second 0 (place holder for the missing x term) and add to get 125.  5 * 125 = 625.  And then subtract 4 from that to get a remainder of 621.  Obviously x - 5 is not a factor!