40.21. a) 3√7 - 4x = 3 ;

а) $$3√7 - 4x = 3$$.

$$3\sqrt[3]{7 - 4x} = 3 \implies \sqrt[3]{7 - 4x} = 1 \implies 7 - 4x = 1 \implies -4x = -6 \implies x = \frac{3}{2} = 1.5$$.

Ответ: 1.5