Answer:
...x = age Monica
in 10 years it will be x+10 and it will be three times more than four years ago,
4 years ago she had (x-4)
and as in 10 years it will have 3 times that 10 years ago we write:
x+10 =3(x-4)
x+10 = 3x-12
x-3x=-12-10
-2x=-22
2x =22
x= 11
Monika is 11 years old