Answer:
510
Explanation:
1ml=0.001L
so lets take "x" as the amount of ml that 0.5 liters equal:
x ml=0.5L
cross multiply:

0.5=0.001x
x=500
so 500ml=0.5l
add 10ml of cough syrup to 500 ml of water to get TOTAL liquid quantity:
500+10=510
510 ml
Hope this helps!