This is a linear growth problem and can be solevd by the equation y=mx+b, where m = growth rate (and this is what we have to find here), x= time and b = value at time zero. Therefore at 4 year: y = 4m+4 At 6 year: y = 6m + 4 It says at 6 year it was 1/5 taller than 4th, so: 6m+4 = 4m+4 +1/5(4m+4) So...