Gordon serves 20 x 7 = <<20*7=140>>140 meals in his first restaurant per week.
He serves 40 x 7= <<40*7=280>>280 meals in his second restaurant per week.
At the third restaurant, he serves 50 x 7 = <<50*7=350>>350 meals per week.
Therefore, he serves 140 + 280 + 350 = <<140+280+350=770>>770 meals in total per week.
#### 770