Can you replace the question mark with the correct number?

Why are televisions attracted to people?

Two boys wish to cross a river. The only way to get to the other side is by boat, but that boat can only take one boy at a time. The boat cannot return on its own, there are no ropes or similar tricks, yet both boys manage to cross using the boat.

How?

At my favorite fruit stand,
an orange costs 18,
a pineapple costs 27,
and a grape costs 15.
Using the same logic, can you tell how much a mango costs?

It comprises roots which nobody sees,
Much taller than those trees,
Up and up it goes,
Still it never grows?

There’s a girl who has a large family. She has an equal amount of brothers and sisters, but each brother only has half as many brothers and sisters. What’s the correct amount of brothers and sisters?

Can you identify the hidden rebus in the image below?

There is a box full of marbles,
all but two are blue,
all but two are green,
and all but two are red.

How many marbles are in the box?

What goes through cities and fields, but never moves?

If six children and two dogs were under an umbrella, how come none of them got wet?