Typically, the  key to the proof is to write 1 = <i> ms + nt</i>. For 
example,  
if 
you have a group element <i>a</i> you may write it in the form  <i> a = 
a<sup>ms + nt</sup> = a<sup>ms</sup>a<sup>nt</sup></i>, which 
will usually solve the problem you are given.