Can someone tell me the answer and explain how you got that answer so i can do future problems on my own?

You will FOIL this out like you would any other set of binomials that need to be multiplied.  Begin by multiplying the 7 and the 2 to get 14.  Then go back to the 7 and this time multiply it by -3i to get -21i.  Then move to the 4i.  4i times 2 is 8i.  Then go back to the 4i and multiply it by -3i to get -12i^2.  Putting all that together we have 14-21i+8i-12i^2.  Combine like terms to simplify a bit before we deal with the i^2 term.  14-13i-12i^2.  i^2 = -1, so let's make that substitution.  14-13i-12(-1).  Doing that multiplication we have 14-13i+12.  We can combine like terms once more to get 26-13i as our final answer.  First choice above.