Mathematics: i need with this geometric progression question. just informing the methods is very appreciated!

(a) the first term of a convergent geometric progression is 3. the sum of the first five terms of the progression is twice the sum of the first ten terms. find the sum to infinity of the progression, correct to 3 decimal places. [5 marks]

(b) the salary scale of a certain employee begins at rm60 000 a year and rises to a maximum of rm78 000 by fifteen annual increments of rm1200 each. after the maximum has been reached, the annual salary remains constant. find the amount received by an employee in 20 years.

it is proposed to revise the salary scale so that it begins at rm62 000 a year and every year the salary is increased by 3% of the previous year. how many years would it take
for the total salary on the new scale to be as nearly as possible equal to the total amount received in twenty years on the old scale? [6 marks]