You can use a rule of three to find speeds in percentages above 25%, for example:
77W at 45% load
It is a value that is between 25% and 50%, with a difference of 20% to 25% (45 - 25 = 20%) and 17 kts (148 - 131 = 17 kts) between the “flare” speeds at these two load values.
I believe this would be Vref, but the guide describes it differently.
Source: Unofficial Takeoff and Landing Profiles [777 Family]
Transforming this 25% range that the guide shows into 100%, and dividing 20/25:
45% load = 80% of this range; and calculating 80% of 17 kts = 13.6 kts.
Adding the flare speed at 25%: 131 + 13.6 = 145 kts rounded off!
If you have any doubts, let me know!