Question 1080406
there is no given option that is solution, it should be

he already have {{{120}}}, in three months he has {{{300}}}

the difference is {{{180}}}

each month same amount, means {{{180/3=60}}} is monthly deposit

so,

{{{s=60m+ 120}}}....only this way you have in {{{m=3}}} months {{{300}}} 

check:

{{{s=60*3+ 120}}}

{{{s=180+ 120}}}

{{{s=300}}}