Calculate: 3a+4+5a-2=3

Expression: $3a+4+5a-2=3$

Collect like terms

$8a+4-2=3$

Subtract the numbers

$8a+2=3$

Move the constant to the right-hand side and change its sign

$8a=3-2$

Subtract the numbers

$8a=1$

Divide both sides of the equation by $8$

$\begin{align*}&a=\frac{ 1 }{ 8 } \\&\begin{array} { l }a=0.125,& a={2}^{-3}\end{array}\end{align*}$