2?5+3?7. This is my summer holiday homework question. Seems like it is wrong as in place of plus there should be multiply sign.

Solution 
Assuming your question as " $2\mathrm{\pi }5+3\mathrm{\pi }7$ "
Here, taking $\mathrm{\pi } \mathrm{as} \mathrm{common}, \mathrm{we} \mathrm{get},$
= $\mathrm{\pi }\left(2\times 5+3\times 7\right)=\mathrm{\pi }\left(10+21\right)=31\mathrm{\pi }$

OR "if there is × sign, then
2 × 5 + 3 × 7
According to BODMAS rule,
(2 × 5) + (3 × 7) = 10 + 21 = 31
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