Question 578083
let r = R's age
let b = bro's age
:
Riza is 25 years old while her brother was born.
From this statement we can say:
r = b + 25
:
Now the sum of their ages is 105, what is their present age? 
r + b = 105
replace r with (b+25), find b 
(b+25) + b = 105
2b = 105 - 25
2b = 80
b = 80/2
b = 40 yr is brother's present age
then
25 + 40 = 65 yrs is Riza's present age
:
:
Check this by adding up their ages, and seeing it equals 105