A jar contains 35 coins made up of 20c and 50c coins only. Then total value of the coins is
$13.90.

(I) If there were x 20c coins, write an equation in x for the number of 50c coins.

(ii) Using the given information, write an equation in terms of x for the total sum of money
the jar holds.

(iii) Solve the equation to find the number of each type of coin in the jar.