Hello!
Is the Radius 5 cm? If so then:
The surface area of the cone is calculated through the equation,
A = πr² + πrl
where r is the radius and l is the slant height. Substituting the known values to the equation,
43.75π = π(5 cm)² + π(5 cm)(l)
l is 3.75 cm. Thus, the slant height of the cone is 3.75 cm.
Hope this Helps! Have A Wonderful Day! :)