Ian is able to earn $18 per hour doing surveys. If he worked 8 hours doing surveys, then he earned $18*8 = $<<18*8=144>>144
If he spent half of what he earned, then he spent $144 * 50% = $<<144*50*.01=72>>72
If Ian spent $72 of his earnings, then he has $144 - $72 = $<<72=72>>72 left
#### 72