Is there a diagram with this question?
Literal equation:
we know that
literal equation is equation of more one variable
for example: 
And we can solve such equations only if we are given two such equation
because it has two variables
One variable equation:
such equation has single variables
for example:

we don't need any other equation
we can solve for variables from single equation itself
because it has only one variable that is x
Answer:
It went down 5.5°C a minute.
Step-by-step explanation:
You have to look for the difference of 100 and 78, which is 22.
Divide the difference with the minutes (4), equalling 5.5.