v1=8;
v2=20;
r1=1;
r2=2;
r3=3;
r4=4;
r5=5;
i1=2;
vx=(i1-v2/r5+v1*r4*(1/r4+1/r5)/(r1+r2))/((1/r3+1/r4+1/(r1+r2))*(1/r4+1/r5)*r4-1/r4);
vy=r4*((vx*(1/r3+1/r4+1/(r1+r2)))-v1/(r1+r2));
i4=(vx-vy)/r4;
disp("the current (in mA) flowing through R4 is"); disp(i4);
disp("and the direction is left to right");