Noah and Ava’s zoo entry tickets are $5 x 2 = $<<5*2=10>>10.
Their round trip bus fare will be $1.50 x 2 x 2 = $<<1.5*2*2=6>>6.
Zoo tickets and bus fare will cost $10 + $6 = $<<10+6=16>>16.
For lunch and snacks, they will have $40 - $16 = $<<40-16=24>>24.
#### 24