Question 818814
Let:
x=age of her sister
2x+1= age of monica

Solution:

age of monica - age of her sister = 18

{{{ (2x+1) - x = 18}}}
{{{ 2x-x =18-1 }}}
{{{ x =17 }}} age of her sister

{{{ 2x+1}}}= age of monica
{{{ 2(17)+1}}
{{{ 34+1}}}
{{{ 35 }}}= age of monica

Final Answer:

Age of Monica is 35.
Age of her sister is 17.