Question 1018976
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Five years ago, David {{{highlight(cross(is))}}} was 4 times as old as Anna. The present sum of their ages is 25. What are {{{highlight(cross(these))}}} their ages?
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Let D = David's present age, A = Anna's present age.

Five years ago David's age was D-5, while Anna's age was A-5, 
and the condition says that

D-5 = 4*(A-5).

This is your first equation.

The second is

D + A = 25.

Now express D = 25 - A from the second equation and substitute it into the first. You will get

(25-A) - 5 = 4*(A-5).

Simplify and solve it:

30 - A = 4A - 20,

20 + 20 = 4A + A,

5A = 40,

A = {{{40/5}}} = 8. 

Thus Anna is 8 years now. 
Hence, David is D = 25 - A = 25 - 8 = 17 years now.
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