The relation between $16$ and $49$ $= 16*3 + 1,$ if $i$ sum then it is $49$
The relation between $29$ and $89$ $= 29*3 + 2,$ if $i$ sum then it is $89$
th relation between X and $147$ $= x*3 + 3,$ if $i$ sum then it is $147$
hence, $3X + 3 =147$
$X = 48$