Answer:
![20x+10y\ge 2000](https://img.qammunity.org/2020/formulas/mathematics/middle-school/q4h5mp55aqqt09omvk4aiyf5ae34uzyl6g.png)
Explanation:
Let x represent the number of lawns Jacob mowed and y represent the number of dogs Sarah walked.
Jacob charges $20 each time he mows a lawn, then he earns $20x for x lawns mowed.
Sarah charges $10 each time she walks a dog, then she earns $10y for y dogs walked.
In total, they will earn $(20x + 10y). They need at least $2000 in order to go on a trip, then
![20x+10y\ge 2000](https://img.qammunity.org/2020/formulas/mathematics/middle-school/q4h5mp55aqqt09omvk4aiyf5ae34uzyl6g.png)
Note that
![x\ge 0,\ y\ge 0.](https://img.qammunity.org/2020/formulas/mathematics/middle-school/rs717jtyyl80np3xdojhnskaog8lijd96q.png)