If you need 10 mins (1 standard row), it costs 25 or 2.5 each;

if you need 20 mins (2 standard rows), it costs 60 or 3.0 each;

if you need 30 mins (3 standard rows), it costs 105 or 3.5 each;

if you need 40 mins (4 standard rows), it costs 160 or 4.0 each;

in other words, for each extra row, the unit cost goes up by 0.5 ecs.

if you need 20 mins (2 standard rows), it costs 60 or 3.0 each;

if you need 30 mins (3 standard rows), it costs 105 or 3.5 each;

if you need 40 mins (4 standard rows), it costs 160 or 4.0 each;

in other words, for each extra row, the unit cost goes up by 0.5 ecs.

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