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Workings

Hint
A little bit of algebra might help.

Answers
Drew is 7 years old. Glen is 4 years old.
Answer #1
The first question involves Drew (D) and Alex (A).

Drew is currently one fifth of Alex's age, so:

(1)      A = D x 5

In 21 years, Alex will be twice their age, so:

(2) A + 21 = (D + 21) x 2

Using (1) in (2) gives:

  A + 21 = (D + 21) x 2

 5D + 21 = (D + 21) x 2

 5D + 21 = 2D + 42

      3D = 21

       D = 7

So Drew is 7 (and Alex is 35).

Answer #2
The second question involves Glen (G) and Billie (B).

Billie is exactly seven times the age of Glen:

(3)     B = G x 7

In 8 years, Billie will be three times the age of Glen, so:

(4) B + 8 = (G + 8) x 3

Using (3) in (4) gives:

  B + 8 = (G + 8) x 3

 7G + 8 = (G + 8) x 3

 7G + 8 = 3G + 24

     4G = 16

      G = 4

So Glen is 4 (and Billie is 28).

Workings

Hint
Do leap years make a difference?

Answer
Hours in 10 years.

Reasoning
In a day, there are 60 x 60 x 24 seconds = 86,400 seconds.

In 10 years, there are 10 x 365 x 24 hours = 87,600 hours, which even without the leap years is already the larger number.

Workings

Hint
One of the words is Antelope.

Answer
ln      =  lion
ntlp    =  antelope
gzll    =  gazelle
strch   =  ostrich
wl      =  owl
rbn     =  robin
rdvrk   =  aardvark
dr      =  deer
clt     =  ocelot or colt
bs      =  ibis

Workings

Hint
How many pieces on the top layer had two sides with icing?

Answer
15 pieces.

Reasoning
On each layer there are 4 pieces with exactly two sides of icing.

Therefore Kevin ate 12 pieces, leaving 15 for the guests.