Two digit number $$=12,16, 20, 24........96$$
Hence, it is making the AP series $$12+16+20+........96$$
$$n=24-2=22$$
$$d=4$$
$$a=12$$
$$S_n=\dfrac{n(2a+(n-1)d)}{2}$$
Hence, the required sum $$S_n=\dfrac{22(2\times 12+(22-1)\times 4)}{2}$$
$$\Rightarrow S_n=11\times (24+84)$$
$$\Rightarrow S_n=11\times 108$$
$$\Rightarrow S_n=1188$$
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