Three years ago, sherman was twice as old as clive. if clive’s present age is c, which expression represents sherman’s present age in terms of clive’s age?

First establish variables for current age.

Clive's current age = c
Sherman's current age = s

"Three years ago," 
Clive was: (c - 3)
Sherman was: (s - 3)

"Sherman was twice as old as Clive."
(s - 3) = 2(c - 3)

Then in terms of Sherman's present age, distribute 2, combine like terms
s - 3 = 2c - 6
s = 2c - 6 + 3
s = 2c - 3