On a 30øC day, there is an explosion. The sound is heard 3.4 s after seeing the flash. How far..?

Question

away was the explosion?

Answer 1

speed = distance / time and
distance = speed*time

You need to find the speed of light, c. The temperature doesn't matter here. And find the speed of sound, vs, at 30oC. The light and the sound travel the same distance, so
c*tlight = vs*tsound

Now the trick is that tsound isn't 3.4 s. Because the sound started at the same time as the light. The sound was partway to you when the flash reached you (after time tlight), then it was another 3.4 seconds. So
tsound = 3.4 s + tlight.

So you have 2 equations in 2 unknowns. I think you can take it from here.

Answer 2

What's with all the explosions? 3 of the last 4 physics questions are related to explosions. You know, we physicists do more than blow things up. It the Manhattan Project, wasn't it? Anyway, we prefer the term "rapid dissassembly" :-)