No verified figure fixes how much line to carry for the 75 ft task. What the task does fix is the start and the finish: the fly begins no farther than 50 ft out and has to land at least 75 ft away with a relatively straight leader, so everything beyond the start comes from building the carry and shooting on the delivery.

Establish the measurement convention before you pick a number. Check whether the 75 ft is measured from the caster or from the rod tip, and whether the leader and the rod’s reach are included; a mark measured from your feet leaves less line to shoot than one measured from the tip.

Then carry the longest line you can keep controllable and shoot the rest. Getting there from a 50 ft carry means changing the cast, not pushing harder:

• The line must go faster, so the rod speeds up — more force over the same distance, or a similar force over a longer distance, which is easier to control and less likely to tail.
• A faster, more deeply bent rod needs a wider casting arc to keep the rod tip path straight, and lengthening the stroke widens the arc at the same time. An open stance, casting-side foot back, helps.
• Hauling is encouraged here, and a longer carry usually takes a longer haul.
• Keep loops stable, hauls consistent and slack out of the false casting. Avoid last cast syndrome: extra force on the delivery tails and loses the cast.

Source

From Task 15 in the CI Study Guide (2025) (PDF); terms from the FFI Fly Casting Definitions (False Cast, Casting Arc). See also Task 15, distance to 75 ft.