Question

Evaluate 15/r -1 when r = 5

Answer 1

$\frac{15}{r}-1=\frac{15}{5}-1=3-1=2$

2)
$\frac{15}{r-1}=\frac{15}{5-1}=\frac{15}{4}=3\frac{3}{4}=3.75$

Answer 2

15/r-1  
15/5-1  (substitute 5 for r)
15/4     (5-1 is 4)
3.75     (15/4 is 3.75)