Sorry this is all such a mess - I
haven't used it for a long time and it needs a major spring-clean!
And I need to work out how to use new (to me) authoring software.

Plot a graph of stretching force in newtons (vertically) against
extension in metres (horizontally). Find the 'area' under this
graph by counting squares or by approximating to rectangles,
triangles and trapezia. This 'area' is the work done, and is equal
to the KE imparted to the missile. Use KE = ½

mu²
to find the initial velocity

u.

Plot range (vertically) against launch angle (horizontally) to
determine the maximum range and the angle φ for maximum range. Use
the formula

R
= *u*² sin2φ / g

and compare with the measured value of

R