\[\boxed{\text{917\ (917).\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[4x + 3y = 30;\ \ A\ (6;b)\]
\[4 \cdot 6 + 3 \cdot b = 30\ \]
\[3b = 30 - 24\ \ \]
\[3b = 6\ \]
\[b = 2\]
\[Ответ:b = 2.\]