Equation 1 

Human = eat + sleep + work + enjoy
Donkey = eat + sleep

Therefore:
Human = Donkey + Work + enjoy

Therefore:
Human-enjoy = Donkey + Work

In other words,
A Human that doesn't know how to enjoy = Donkey that works. 

++++++++++++ +++++++++ +++++++++ +++++++++ +++++++++ ++ ++ 

Equation 2 
Man = eat + sleep + earn money
Donkey = eat + sleep

Therefore:
Man = Donkey + earn money

Therefore:
Man-earn money = Donkey

In other words
Man who doesn't earn money = Donkey 

++++++++++++ +++++++++ +++++++++ +++++++++ +++++++++ +

Equation 3 

Woman= eat + sleep + spend
Donkey = eat + sleep

Therefore:
Woman = Donkey + spend
Woman - spend = Donkey

In other words,
Woman who doesn't spend = Donkey

++++++++++++ +++++++++ +++++++++ +++++++++ +++++++++ +

To Conclude:

From Equation 2 and Equation 3

Man who doesn't earn money = Woman who doesn't spend

So Man earns money not to let woman become a donkey!
And a woman spends not to let the man become a donkey!

So, We have:
Man + Woman = Donkey + earn money + Donkey + Spend money

Therefore from postulates 1 and 2, we can conclude 

Man + Woman = 2 Donkeys that live happily together