let 'x' be the age of the son
'y' be the age of the father(Mr. Belen)
since Mr. Belen is 30 yrs older than his son then,
y = x + 30 ----equation 1
and given that Mr. Belen is 10 more than thrice as old as his son then,
y = 3x + 10 ---equation 2
equate 1 and 2
3x + 10 = x + 30
3x - x = 30 - 10
2x = 20
x = 10
substitute to equation 1
y = x + 30
y = 10 + 30
y = 40
therefore Mr. Belen is 40yrs old while his son is 10yrs old.