How would i figure out 19 and 20?

Smaller diagonal is 4.453 and longer diagonal is 10
If the two sides of a parallelogram are a and b and acute angle between the sides is θ,

the smaller diagonal is √a2+b2−2abcosθ

and longer diagonal is √a2+b2+2abcosθ

Hence in the given case

Smaller diagonal is √3.72+6.82−2×3.7×6.8×cos48∘

= √13.69+46.24−50.32×0.66913

= √59.93−40.101

= √19.829

= 4.453

Longer diagonal is √3.72+6.82+2×3.7×6.8×cos48∘

= √13.69+46.24+50.32×0.66913

= √59.93+40.101

= √100.031

= 10

18