First of all, you need to know what the beta coefficient expressed by financial engineering is for.

When investing, the dispersion degree of the probability distribution of possible results is called risk, so we can use beta coefficient and variance (standard deviation) to measure investment risk.

Beta coefficient is a measure of the average fluctuation degree of the return of investment tools relative to the market in the same period.

So the formula is

Beta coefficient = (expected rate of return on investment instruments-risk-free part of return)/(expected rate of return on the whole market-risk-free part)

So the problem is beta = (10%-4%)/(20%-4%) = 37.5%.