Lilianna uses \dfrac{3}{4}
4
3
​
start fraction, 3, divided by, 4, end fraction calories per minute just by sitting. She uses 111 more calorie per minute by walking. Lilianna uses a total of 12\dfrac{1}{4}12
4
1
​
12, start fraction, 1, divided by, 4, end fraction calories walking to the park.
Lilianna uses the equation, d\left(\dfrac{3}{4}+1\right)=12\dfrac{1}{4}d(
4
3
​
+1)=12
4
1
​
d, left parenthesis, start fraction, 3, divided by, 4, end fraction, plus, 1, right parenthesis, equals, 12, start fraction, 1, divided by, 4, end fraction to represent the situation.
What does the variable ddd represent in the equation?