Can you please help me? I'll mark brainiest

The boy of mass 30 kg is at r1= 2 meters from the fulcrum. of the girl is 45 kg, at what r2 must she sit so that they are balanced ?

There are two-speed cameras, one in an are where the speed limit is 30 km/h and another where the speed limit is 50 km/h. in which will there be a smaller time interval between the photographs? explain your answer.

A10nc charge sits at a point in space where the magnitude of the electric field is 1500 n/c. what will the magnitude of the field be if the 10 nc charge is replaced by a 20 nc charge? assume the system is big enough to consider the charges as small test charges.