Need Help w/ Physics, Current, Resistance, Potential?

Question

i need help w/ Lab exercise 2

http://class.phys.psu.edu/212Recitations/07_Circuits/DC_Circuits.pdf

Answer 1

I1(20 + 20) - I2(20) = 9 + 9
-I1(20) + I2(20 + 10)= -9 - 9

40 I1 - 20 I2=18
-20 I1 + 30 I2=-18

40 I1 - 20 I2=18
-40 I1 + 60 I2=-36

40I2=-18
I2= -18/40 =0.45A

40 I1 - 20 I2=18
I1=(18+20I2)/40
I1=(18 + 20 (.45))/40
I1=.675A