A cylindrical brass pin 2.50 cm long and 0.400 cm in diameter (ends masked) is plated sequentially with nickel (from Ni2+) and then chromium (from Cr3+) using the same constant current of 2.20 A for a total of 18.0 min. Exactly 60.0 % of the total charge is used for nickel deposition and the remainder for chromium. The densities of nickel and chromium are 8.90 g cm−3 and 7.19 g cm−3, respectively. Calculate the thickness of each metallic layer in micrometres.