Question 332969
Let  vial of Humulin insulin  be X
and
vial of Novolin Velosulin insulin be Y
 X+Y=50
x=50 -Y--------------->(1)
cost of vial of Humulin insulin =$27.06
cost of vial of Novolin Velosulin insulin  = $34.39
total cost = $1565.57
ie,
$27.06X +$ 34.39 Y =$1565.57-------------->(2)
from (1)we know 
X=50-Y

$27.06(50-Y) +$34.39Y= $1565.57
27.06*50 -27.06Y +34.39Y =1565.57
1353 +7.33Y=1565.57
7.33Y=1565.57 -1353
7.33Y= 212.57
Y= 29
x=50-Y
x=50-29 =21

Number of Humulin insulin =21
and 
Number of  Novolin Velosulin insulin  =29