Solution :
Let the number be $a$ and $b$.
$\therefore$ According to question,
$a+b=29$...(1)
and $a^{2}-b^{2}=145 \quad$...(2)
We know that,
$$
\begin{aligned}
& a^{2}-b^{2}=(a+b)(a-b) \\
\Rightarrow & 145=29(a-b) \\
\therefore \quad & a-b=\frac{145}{29}=5 ; \text { Ans. }
\end{aligned}
$$