Explanation:
she has x money at the beginning.
(3/4)x = dictionary
the remainder is (1/4)x.
1/2 of that (1/4 × 1/2 = 1/8) is the calculator.
that means she has (1/4)x - (1/8)x = (1/8)x left.
the dictionary is $30 more than the calculator.
so,
(3/4)x = (1/8)x + 30
(6/8)x = (1/8)x + 30
(5/8)x = 30
5x = 240
x = 240/5 = $48
so, the dictionary cost
(3/4)x = (3/4)×48 = 3×12 = $36