$\"\"$

\

The equations are

\

$\"\"$ (Equation (1)

\

$\"\"$ (Equation (2)

\

Solve the equation 2 for variable c in terms of the variable d.

\

$\"\"$

\

$\"\"$ (Subtract 3d from each side)

\

$\"\"$ (Apply additive inverse property: $\"\"$ )

\

$\"\"$

\

Substitute $\"\"$ for c in equation 1.

\

$\"\"$

\

$\"\"$ (Distribute 4)

\

$\"\"$ (Simplify)

\

$\"\"$ (Add: $\"\"$ )

\

$\"\"$ (Subtract 40 from each side)

\

$\"\"$ (Simplify)

\

$\"\"$ (Divide each side by -10)

\

$\"\"$ (Divide: $\"\"$ )

\

$\"\"$

\

Substitute $\"\"$ for d in $\"\"$ .

\

$\"\"$

\

$\"\"$ (Simplify)

\

$\"\"$ (Subtract: $\"\"$ ) $\"\"$

\

The solution is $\"\"$ .

\