Try integrating the solution to u'[x] + 5u[x] == 0 (u[x] = y'[x]). Of course -1/5 * C[1] is an arbitrary constant, and so may be replaced by single parameter.
u'[x] + 5u[x] == 0
u[x] = y'[x])
-1/5 * C[1]
