Help me please I dont know this

In the field of thermodynamics, rankine is the unit used to measure temperature. one can convert temperature from celsius into rankine using the formula c= r/1.8 - 273, what is the temperature in celcius corresponding to r degrees rankine.

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?

One file clerk can file 10 folders per minute. a second file clerk can file 11 folders per minute. how many minutes would the two clerks together take to file 672 folders?