Sea
H : Las horas que tardaría.
Resolviendo
Vamos a utilizar una regla de tres simple inversa : = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Litros por Min : Horas : 18 14 7 H = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
Tenemos magnitudes inversamente proporcionales, entonces multiplicamos los valores horizontamente para armar nuestra ecuación :
<img src="https://tex.z-dn.net/?f=7H%3D%2818%29%2814%29%5C%5C%20%5C%5C7H%3D252%5C%5C%20%5C%5CH%3D%20%5Cdfrac%7B252%7D%7B7%7D%5C%5C%20%5C%5CH%3D%5Cboxed%7B36%7D%5Cquad%5Ccheckmark%5C%20Las%5C%20horas%5C%20que%5C%20tardar%5C%27ia.%5C%20%5Cmathbb%7BRESPUESTA%7D" />
MUCHA SUERTE!