Let EB be Eng Bok and F be Fred.
And let u represent 'units'
At first:

EB= 6u
F= 1u

End:
EB= 70 sheets of paper
F= 70 sheets of paper

since the total is 7u (6u+1u), an equal number of sheets of paper each (70 sheets of paper each) means:
EB= 3.5u
F= 3.5u

Hence, 3.5u= 70
1u= 70 ÷3.5
= 20
Sheets of paper EB has to give to F = 6u-3.5u= 2.5u
2.5u = 20×2.5
= 50
Ans: 50

Hope this is correct!! :)

The above method and answer is correct.

A slightly different approach :

Eng Bok : 6 units
Fred : 1 unit

Total : 7 units

if they each have 70 sheets,

Total = 70 + 70 = 140 sheets

Notice the total doesn't change.

So 140 sheets = 7 units

1 unit = 140 ÷ 7 = 20 sheets

So Fred has 20 sheets (1 unit)

Number of sheets Eng Bok must give to Fred
= 70 - 20
= 50 sheets.