Question

I_ your younger brother yesterday (meet/will meet/met)

Answer 1

$\bf { \underline{ \underline{ \green{Question}}}}$

→ I_ your younger brother yesterday (meet/will meet/met)

$\bf { \underline{ \underline{ \green{Answer}}}}$

→ I met your younger brother yesterday.

In the given sentence yesterday is given as a time phrase which yours that the sentence is referring to past tense .

In the given option met is the second form of verb, and in past simple tense we use second form of verb so met will be the answer.