There are two ways to do this problem:

First way:

One worker earns £x
The other earns £300-£x

So £x = £300-£x + £25
    x = 300 - x + 25
    x = 325 - x
   2x = 325
    x = 162.50

One worker earns £x = £162.50
The other earns £300-£x = £300-£162.50 = £137.50

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Second way:

Other worker gets £x
So the one worker gets £x + £25

Therefore the equation is

£x + £x + £25 = £300
   x + x + 25 = 300
      2x + 25 = 300
           2x = 275
            x = 137.50

So

The other worker gets £x = £137.50
The one worker gets £x + £25 = £137.50 + £25 = £162.50

Edwin