Let's suppose that
$$10,a+15,ba +15,3 = 2\times (20, ab)$$
where numbers are in their decimal representation, and so $ab$ and $ba$ are two digit numbers. Is there a straightforward way to evaluate $a\times b$? One approach is to write down
$$10+\frac{a}{10}+15+\frac{10b+a}{100}+15+\frac{3}{10} = 2\times (20+\frac{10a+b}{100})$$
You are on the right track. The next step is to simplify the expression. The expression simplifies to
$$\frac{3}{10} - \frac{9}{100} a + \frac{8}{100} b = 0$$
and this simplifies further once you multiply it by $100$ to
$$9a-8b=30$$