If
an implies s
ef implies i
gh implies m
then ns implies ?

the options are :
1)t
2)a
3)l
4)k

If you reverse the first two letters
Na
Fe
Hg
Sn

They are actually symbols for elements
Na - Sodium
Fe - Iron
Hg - Mercury
Sn - Tin

Since Sn is a symbol for Tin and each pair of letters imply the starting letter of the element they are symbolizing, the answer is
1) T

You can find the area of a rectangle by multiplying the length and height. so multiply 1/2*7/4(which is the simpler version of 1 3/4) and you get 7/8 as your answer.