I must admit, I'd usually all of this with a calculator and look-up table, but let's use the CRP-1 in my flight bag.
First G/S, you need to know your minimum groundspeed. That is
77*60/42 = 110 kts Much easier on a calculator, but just using the outer rings as circular slide rule is easy enough in two stages.
77 x 60 = 4620, rotate the cursor around to that value. Now rotate 42 on the inner ring to line up with the cursor, look at the 10 on the inner ring, and it lines up with 11 on the outer ring. There's your 110kts.
If I turn the Airspeed window so that +10deg.C lines up with 5,000ft I can see a density altitude of 6,000ft-ish in that window. That's intuitively correct as ISA for 5,000ft would be 15deg.C minus (5 * 2) = 5 deg.C, so we're above ISA, and therefore the air is less dense, increasing the density altitude.
Now looking to the outer ring, against 11 on the outer ring, I can see 10.15 on the next ring in. That maps G/S in zero wind to CAS - so 101.5 kts.
So, I need 101.5kts CAS to reach my destination in 42 minutes. I'd call it 102kt to play safe.
G