Answer:
1.for the first one 100centimeters make 1 meter therefore
100cm-1m
340cm-x
340/100
=3.4
the answer is supposed to be 3.4, maybe there's a mistake with the question or the answer
2.the weight of a body is given by the formula
mass×gravity,in this case the mass is 75kg and the gravity is 9.8
weight=75×9.8
=735N
3.for this one the mass of a body is given by the formula
mass=weight/gravity
=420/9.8
=42.8kg
I hope this helps