Good news. I have owned a 2015 model from new. It has now done 44,000 miles ++. 100Km is 62 miles. That should technically be okay. Driving at 62mph is also okay in a PHEV.
Answer to 1: For 62 miles, you should still have some battery left [regardless of what the display tells you]. So for 62 miles, with a full charge at the start of your journey, you should achieve around 50mpg of petrol, [which includes the batteries].
Answer to Q2: Travelling at 50km which is 31.069miles, you should be able to get 140 to 150 miles per gallon with a full charge. ~At a speed of 62 miles for half of it, you should get around 50 to 70 mpg.
FACT: If your speed does not exceed 50mph, you should get 140 mpg for 32 miles, and evening it out as in Question 2, you should attain 140 to 200mpg if you travel some bits at urban speed, and some at highway speed provided it does not exceed 50mph.
Anything above 60 mph eg at 70mph, the above facts will not apply. At 70mph, your battery will exhaust in 8 to 10 miles, amd after that you a looking at 28 to 31 mpg.
Afteral at 70mph, the air becomes thick and it is like driving through water. At 120mph, the air will be akin to treacle..and you might get arrested for exceeding the speed limit!
Any problems come back to me.