Rhys,

I did it this way:

4a + 2B = 100

So........ 4a = 100-2b

.... a = 25-1/2b

Which means:

4(25-1/2b) + 6b = 181

Mutiply out.........

100-2b+6b = 181

100+4b = 181

4b = 81

b = 20.25

Then just input that into the other equation:

4a + 40.5 = 100

4a = 59.5

a = 14.875


All I keep seeing is that line at the top of the exam paper that says:

"Don't forget to show ALL your work"