betfair:

-44.10 / 2.10 = -21
16.91*0.947 / 6.6 = 2.426

-21 + 2.426 = -18.574

matchbook:

48.65*0.97 / 2.12 = 22.259
1.90*0.97 / 6.5 = 0.283

22.259 + 0.283 = 22.542

overall

-18.574 + 22.542 = 3.968