The second tomato plant bore 8 + 4 = <<8+4=12>>12 fruit.
The first two plants bore 8 + 12 = <<8+12=20>>20 fruit combined.
Each of the other two plants bore 20 x 3 = <<20*3=60>>60 fruit.
Mabel has 8 + 12 + 60 + 60 = <<8+12+60+60=140>>140 tomatoes
#### 140