in which f and k are known functions, and φ is to be determined. since the unknown function φ appears under an integral sign, the given equation is called an integral equation; in particular, it belongs to a class of integral equations known as volterra integral equations7. take the laplace transform of the given integral equation and obtain an expression for l{φ (t)} in terms of the transforms l{ f (t)} and l{k(t)} of the given functions f and k. the inverse transform of l{φ (t)} is the solution of the original integral equation