Question 205213
Let b be the age of the son
let r be riza's age
{{{r = b + 25}}}
Given {{{r + b = 105}}}
{{{(b+25) + b = 105}}}
{{{2b + 25 = 105}}}
{{{2b = 80}}}
{{{b = 40}}}
Her boy is not 40. Since she is 25 years older than he, Riza must be 65. 

Just don't tell her friends, Riza tells them she is 51 ;).