Rate problem

Write as a system of 3 equations: 

$r = 8+i$                       (1)

$s = 4r$                            (2)

$i+r+s=96$              (3)

Rearrange (1) so $i$ is the independent variable: $i = r - 8$

Now, substitute i and s in terms of r: $r + 4r + r-8 =96$

Simplify: $6r - 8 = 96$

Add 8 to both sides: $6r = 104$

Divide by 6: $r = 17 {1 \over 3}$

Now substitute $r$ into (1) and solve for $i$: $17 {1 \over3} = 8 + i$

Subtract 8 from both sides: $i = 9 {1 \over3}$

Now substitute $r$ into (2) and solve for $s$: $4 \times 17 {1 \over 3} = s$

Simplify: $s = 69 {1 \over 3}$