Question

a number is sruared and 3times of the number is addad

Answer 1

lets take a number $x$
Square of $x$ = $x^{2}$

And 3 times $x$ = 3$x$

So equation is = $x^{2}$ + $3x$ 

Answer 2

let the number be ' a'
By Data
if we square it then it is $a^{2}$
and 3 times of a becomes 3a
required equation is 
$a^{2}$+3a