if the value of the resistor r2 were doubled, how would the value of the resistor r3 have to change in order to keep the current through r4 equal to zero?

see the picture for the vector

the magnitude of the vector by pythagorean theorem

r = √( (-10)^2 + (3)^2 ) = √109

magnitude = √109 units

the direction angle between vector and x-axis is

tan^(-1)(3/10) = 16.699

so the direction is approximately 16.7 degrees north of west

the ima (higher than 1m) will be greater than the ima with the height of 1m.