Can anyone help me with this?

Possibly fairly simple but I cant for the life of me remember how to do it.

For the circuit below, given that the power dissipated in R5 is 25mW, calculate value of the current source, I1.

**broken link removed**

25mw gives you the voltage across R5 (use Ohm's law for power) which gives you the node voltage for R6,7. Take the sum of R6,7 in parallel with R5, now you can find the current into that node and the drop across R4. This gives you the voltage across R3, etc.