Final answer:
Using the linear function c(t) = 2t + 10 provided in the question, the cost for 3 hours of repair comes to 16 birr. This function is an example of a linear equation used to calculate costs in various service-related scenarios.
Step-by-step explanation:
The student's question involves a linear function, which is a concept from algebra where a formula is used to calculate the cost based on hours of work. In this case, the mobile phone technician uses the linear function c(t) = 2t + 10 to determine the cost of repair, where t is the time in hours and c(t) is the cost in birr. To find out how much it will cost if it takes 3 hours to repair a mobile phone, we simply substitute t with 3 in the equation and solve for c(t).
When we carry out this calculation, c(3) = 2(3) + 10, we get:
c(3) = 6 + 10 = 16 birr. Thus, the technician will charge 16 birr for 3 hours of work. This equation represents a typical example of how linear equations are used to calculate costs in various services, such as repairs and cleaning services. The cost consists of a fixed fee plus a variable fee that depends on the duration of the service provided.