$$\frac{3}{8}a = 0,72b$$
$$\frac{3}{8}a = \frac{72}{100}b$$
$$\frac{3}{8}a = \frac{18}{25}b$$
$$a = \frac{18}{25}b : \frac{3}{8}$$
$$a = \frac{18}{25}b \cdot \frac{8}{3}$$
$$a = \frac{6}{25}b \cdot 8 = \frac{48}{25}b = 1,92b$$
Так как 1,92 > 1, то a > b
Ответ: a > b