There are a number of
questions like this .... normally
use of FIG 4.7.3 would involve you working through the chart from DISTANCE to
WIND to ALTITUDE to WEIGHT and arriving at the FUEL required.
For this question, the requirement is to find the ALTITUDE. To come up with the
answer you need to work normally through DISTANCE and WIND, and then backwards
through FUEL and WEIGHT.
Start at 950nm...to the WIND REF LINE...adjust for
20kt Head. Draw a line straight up through the ALTITUDE section.
Now go to the FUEL scale 5800kg ...we need to work backwards ... (backwards use
of this ref lines needs you to go from 5800kg to the 500000kg condition, then
adjust back to the reference line). Luckily in this example, the weight
condition of 50000kg is the ref line value, hence there is no adjustment
required - all we have to do is draw a line from 5800kg straight through the
ref line and through the altitude section. Your 2 lines should meet at 25000ft.