Hey there! So s substituent with a higher atomic number takes precedence over a substituent with a lower atomic number. If there is a tie like in this case where we all have C directly attached we have to look further in the chain there is a point of difference and apply the first rule. Also double and triple bonds counts as 2 and 3 bonds to carbon respectively. So I'll just assign them as A to D from left to right. The sequence in priority will be D>B>C>A. I hope this helps!