There are three firms (X, Y and Z) supplying a market. The table shows their supply at four different prices.
Which price change is required for market supply to double?

1 )
$\$ 10{\text{ }}to{\text{ }}\$ 20$
$\$ 10{\text{ }}to{\text{ }}\$ 30$
3 )
$\$ 20{\text{ }}to{\text{ }}\$ 30$
4 )
$\$ 20{\text{ }}to{\text{ }}\$ 40$
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