Let x be the distances both people have moved (they move at the same speed so their distances covered must be the same). The distance of 10 km between them is the straight line distance. You will see a right angled triangle.

By the Pythagoras’ Theorem,

x^2 + x^2 = 10^2
2x^2 = 100
x^2 = 50
x = 7.07... km

They walked at 4 km/h, so...

time taken
= 7.07.../4
= 1.7677...
= 1 h 46.066 min

so this occurs at 2:46 pm.

Thank you!!

Ada started walking 1 hr earlier than bob so i think the distance covered arent the same

Ah right. Did not read the noon part.

If no one does this on paper later, I will do the writing at 1 pm. Just woke up several minutes and I am not ready to pen down any writing yet.