[tex] \dfrac{1}{4}(r - \dfrac{5}{2}) = \dfrac{1}{8} [/tex]
The LCD of both fractions is 8, so multiply both sides by 8.
[tex] 8 \times \dfrac{1}{4}(r - \dfrac{5}{2}) = 8 \times \dfrac{1}{8} [/tex]
[tex] 2(r - \dfrac{5}{2}) = 1 [/tex]
Distribute the 2 on the left side.
[tex] 2r - 5 = 1 [/tex]
[tex] 2r = 6 [/tex]
[tex] r = 3 [/tex]