During a 4-month-long drought, the water level in a lake changed by −3 1/2 feet. the water level changed at the same rate each month. what is amount the water level changed in 1 month?

In 4 months, the water level changed in the lake by -3.5 ft.
We want to know the change in one month knowing that the change is the same for all months.
To do that, we can simply do a cross multiplication as follows:
change per month=(1*-3.5)/4 = -0.875 ft

Agreed i also had the same answer