He bikes 4/10 of a mile in 1/5 of an hour
That is 4/10 miles in 1/5 hours
Average speed = Distance/ time = 4/10 ÷ 1/5 = 4/10 × 5/1 = 2 miles/hour
So the ratio of boys to girls is 12:24.. now, is that an equivalent ratio as 2 boys for 4 girls? or 2:4? let's see.

you could start simplifying the 12/24 fraction by dividing by some common multiple, say 2, and get 6/12, then divide by 3 and get 2/4 and stop there.
then you'll notice that 12/24 is really 2/4 in disguise.
Jiri is 22 years old and Pamela is 66
22•3=66
22+66=88
F(-4x)=4x+4x
set up the composite function and simplify!