Answer
96
Work Step by Step
"quotient of y and $3$" $\rightarrow\quad \displaystyle \frac{y}{3}$
"1 less than the quotient of y and $3$" $\rightarrow\quad \displaystyle \frac{y}{3}-1$
"x is 1 less than the quotient of y and $3$" $\rightarrow\quad x=\displaystyle \frac{y}{3}-1$
If y=$15$, we calculate x from the last equation,
$x=\displaystyle \frac{y}{3}-1\\=\dfrac{15}{3}-1\\=5-1\\=4$
To evaluate the expression, replace x with $4$ and y with $15$:
$3x+4(y+6)=$
$=3(4)+4(15+6)$
$=12+4(21)$
$=12+84$
$=96$
