Answer:
Buoyant force = g M / V * V = g d V where d is the mass / volume (density)
Fw = g * Vw * dw buoyant force of water on block (10 N)
Fbr = g * Vw * dbr buoyant force of brine on block
Fbr / Fw = 1.2 buoyant force of brine is 1.2 times that of water
Buoyant force of brine = 10 * 1.2 N = 12 N
Thus, the block will weight 90 - 12 = 78 N submersed in brine
