To solve this problem, we need to determine the value of x, which represents the number of pens that Robert bought.
Let's break down the information given:
Number of pens that Robert bought: x
Number of pens that Julia bought: 3x
Number of pens that Dorothy bought: 1/2 * (3x) = 3/2x
Cost per pen: $1.50
Total amount spent on pens: $33
We can set up the equation as follows:
Number of pens that Robert bought * Cost per pen + Number of pens that Julia bought * Cost per pen + Number of pens that Dorothy bought * Cost per pen = Total amount spent on pens
x * $1.50 + 3x * $1.50 + (3/2x) * $1.50 = $33
Let's simplify and solve for x:
1.5x + 4.5x + 2.25x = 33
8.25x = 33
To isolate x, we divide both sides of the equation by 8.25:
8.25x / 8.25 = 33 / 8.25
x = 4
The value of x is 4.
#### 4
The answer is: 4
Below is a math problem. Provide a detailed, step-by-step solution.

### Problem:
Dorothy, Julia, and Robert go to the store to buy school supplies. Dorothy buys half as many pens as Julia. Julia buys three times as many pens as Robert. Robert buys x pens. If one pen costs $1.50, The three friends spent 33 money in total on pens.

### Answer:
