In order to determine the distance from the point Q until the ground, it is necesary to know the length of the support. It is obtained from the part A of the question, as follow:
d = 5 ft · sin 30° = 2.5 ft
Next, consider, that the line that connects point R and the ground trought Q is the hypotenuse of a triangle. In this case, the length of the support is the adjacent side to the angle 70°. With this information and by using the cosine of the angle 70°, you can obtain the distance from R to the ground trough Q, as follow:
RG: distance from R to the ground (hypotenuse)
cos 70° = length of the support / RG solve for GR
cos 70° = 2.5 ft/ RG
RG = 2.5 ft/ cos 70°
RG = 7.3 ft
Next, to the previous value, subtract the lenght of segment RQ = 5 ft:
Distance from point Q to the ground trough dotted line = 7.3 ft - 5 ft = 2.3 ft
Hence, th answer is 2.3 ft