The three additional lines at T-Mobile cost $16 x 3 = $<<16*3=48>>48.
The total cost of the family plan at T-Mobile is $50 + $48 = $<<50+48=98>>98.
The three additional lines at M-Mobile cost $14 x 3 = $<<14*3=42>>42.
The total cost of the family plan at M-Mobile is$45 + $ 42 = $<<45+42=87>>87.
Therefore, M-Mobile is $98 - 87 = $<<98-87=11>>11 cheaper than T-Mobile.
#### 11