let

c = the number of cans

b = the number of bottles

they collected 150 cans and bottles

c + b = 150 => b = 150 - c

they raised 147 dollars

0.03*c + 0.05*b = 147

if we substitute for b = 150 - c we have

0.03*c + 0.05*(150 - c) = 147

lets solve the equation for c

0.03C + 7.5 - 0.05c = 147

- 0.02c = 147 - 7.5

c = - (147 - 7.5)/ 0.02

c = - 6975 cans

we got c = - 6975 negative number which is not possible since c>0.