The quantity of traveling by train would change by 28%.
Cross-price elasticity measures how the quantity demanded of a good is affected by changes in the price of another good.
Cross price elasticity = percentage change in the quantity demanded of good A / percentage change in the price of good B.
0.7 = percentage change in the quantity of traveling by train / 40%
Percentage change in the quantity of traveling by train = 40 x 0.7 = 28%
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