Solve it if you can

Given that ,

$a = 90$

$b = 90$

Now,

$(a)^2 \times 39 - (b)^2 \times 39$

$90^2 = 8100$

So, $8100 \times 39 = 315900$

$\Rightarrow 8100 \times 29 = 234900$

Now subtract the both,

$\Rightarrow$ $(315900 - 234900) = 81000$

We have, $39a^2 - 29b^2 \Rightarrow 29a^2+10a^2 - 29b^2 \Rightarrow 29(a-b)(a+b) + 10a^2$ Now $a=b=90$ so $a - b =0$ ,Therefore we just have to find the value of $10a^2$ which is $\boxed{81000}$