Find total instruments:
20+20+45+15 = 100
20 are brass
The portion would be number of brass over total:
20/100 which reduces to 1/5 are brass
The answer is D 16a: 1,2,3,4,8,16 and 18ab:1,2,3,46,9,18 a,b
7a+20b = 28-b
7a = 28-b-20b
7a = 28-21b
a= 28/7 - 21/7 b = 4-3b
16 units x 8 units. That’s the answer
