If the plumber chooses the first job, he would earn 3*50 + 3*30 = $<<3*50+3*30=240>>240.
If he chooses the second, he'd earn 2*50 + 5*30 = $<<2*50+5*30=250>>250.
If he chooses the third, he'd earn 50 + 2*40 + 3*30 = $<<50+2*40+3*30=220>>220.
Therefore, the most money he can earn from one of these jobs is $<<250=250>>250.
#### 250