Question

Passive Form of Who had solved his sum?

Answer 1

Heya friend!
It'll be....
His sum had been solved by whom?
OR
By whom was his sum had been solved?
Hope it helps!

Answer 2

$\huge{Hello Mate}$

ACTIVE = $\huge{Who Had Solved This Sum?}$

PASSIVE =By Whom This Sum Solved?

Hope it will help you