Help with problem

[pkomlk pohiu]

Please can anyone help me with this question? The first three terms of a geometric series are (? + 4), ? and (2? − 15) respectively, where ? is a positive constant. Find the sum of the first 30 terms. I am stuck and not able to figure it out. I am tired and about to fall asleep from the exhaustion of working all day. Please any tips or answers would be helpful

 

[Steven G]

What do you multiply k+4 by to get k? What do you multiply k by to get 2k-15? What do you know about these two expressions that you just computed? So what is the value of r?