A potato launcher is launched at a 36 degree angle. The time the potato is in the air is 2.87 seconds and it goes 190 feet. How do I calculate the instant muzzle velocity at which it is launched?

Range = 190 feet = (V^2/g) sin (2*36)

190 = V^2/(32.2) * sin 72

Solve for V, in ft/s

You did not really need to be told the value of time-in-the-air. It was calculable, using
V cos 36 * 2.87 s = 190 ft.

Both methods should give the same answer