The number of grams is calculated by the formula
20C +45A
, where C is number of child doses and A is number of adult doses
Now it says
medical assistant needs to give a dose of the medicine to 12 adults and 10 children
It means we plug C= 10 and A= 12
20(10) +45(12) = 200+540 = 740 grams
change it to kilograms we get
0.74 kilograms
Now doctor needs 0.74 kilograms , but the bottle contains only 0.50 kilograms
So it means It will not be enough and
0.74-0.50 = 0.24 grams
0.24 more grams will be needed