An unknown or changeable quantity is called

The term varies or changes, and often there are restrictions set on the variable (eg: x is positive). Think of a variable as a placeholder for a number.

c = 0.429t

step-by-step explanation:

the constant rate at which carlos harvests cassava is 35 minutes per 15 cassavas 15/35 = 0.429 cassava per minute

therefore, an equation that models the number of cassava (c) that harvest carlos in a time (t) is the following:

where t is the time in minutes.

this means that when 35 minutes have elapsed 15 cassava have been harvested, at 70 minutes 30 cassava have been harvested and so on.

the easiest way to do these would be to solve the equations. if you can solve the equation than you can solve these problems.