Envision the project. If you leave your house at 8am, ½ hour travel time, 2 hours to cut the grass,½ hour travel time back, you have 3 hours invested. If you charge $15 an hour, you will have $30 in your pocket. Ask yourself if you would be happy at 11am when you get back home with 30 dollars in your pocket. If you charge $50 you would have $100 for three hours of your time. Every customer would prefer $100 but if $30 is enough for you, charge $15/hour.
Having said that, set a “mental minimum” so that you feel valued enough during the work that you will do a good job. If you take the job for less than you feel it is worth, it is very difficult to do a quality job. When you perform a job for someone else for money, you sign your name to everything you do for them.
Call 2 lawn care services in the area to get price quotes. If your mental minimum is 15/hour and everyone else charges 75/hour, you could charge 45/hour. The customer gets a great deal and you make good money. Do the same market research with the house cleaning job.
The two other considerations are “parts” and weather this is a one time job or repeating. A repeating job can warrant a discount sometimes. “Parts” include everything you would spend to do the job ie gas, oil, weedeater line, water to drink, snacks, cleaning supplies, buckets, rags, etc. Good Luck, I hope you get the job.