Ihave a math problem. it is 18 ÷ 15.4. would i do 18 ÷ 15 or 18 ÷ 5?

Your question isn't stated in a very clear way so I'm going to show a few possible solutions for the various questions you may be asking.

1.  18 ÷ 15.4
If you can use a calculator just plug it straight in.  No need for the other things that you stated. 
If not, once again do not do 18 / 15 or 18 / 5.  Just do long division.      

2. 18 ÷ 15 (and the 4 is just a typo)
In this case, you should do (18 / 3) ÷ (15 / 3).  This is because the number 3 is common between both 18 and 15.  The answer in this instance would be 6/5, or just Six-fifths  

Ithink it’s d as the answer.

Ican't read this very blury