Spending 40 billion baht on promoting a political party does not directly generate 80 billion baht in sales of other goods and services. The estimate of 70-80 billion baht in related economic activity is based on the idea of the multiplier effect, which is a concept in economics that describes how an initial injection of spending can have a larger impact on overall economic activity.
For example, if a political party spends 40 billion baht on advertising and campaign materials, some of that money will go to companies that produce those materials. These companies will then use some of the money they earned to pay their employees and suppliers, and some of that money will be spent by those employees and suppliers on other goods and services. This chain of spending can continue, with each round of spending generating additional economic activity.
The size of the multiplier effect can vary depending on a number of factors, such as the level of consumer spending and the efficiency of the economy. In this case, the estimate of 70-80 billion baht in related economic activity is based on the assumption that the initial injection of spending by the political parties will have a multiplier effect of around 2, meaning that for every 1 baht spent, an additional 1 baht of economic activity is generated. However, this is just an estimate and the actual impact of the election spending on the economy could be different