Suraj took a slice of pizza from the freezer and put it in the oven. The pizza's temperature (in degrees Celsius) as a function of time (in minutes) is graphed. How long was each increase by 4 degrees Celsius?

We have been given a graph which describes temperature of pizza ( in degree Celsius) as a function of time (in minutes).

We can see that time is independent variable and temperature is dependent variable as it depends on time.  

Let us find when temperature of pizza will reach 0 degree Celsius. We can find the time when temperature will be 0 degrees by finding when y is zero.  

We can see that initial temperature of pizza is about -6 degree Celsius. As time is increasing temperature of pizza is also getting less negative and it is approaching to zero.        

At t= 0.75 minutes our function h(t) equals zero. Therefore, it will take 0.75 minutes the pizza to reach 0 degree Celsius.