Final answer:
The cost of the mobile plan can be represented by the equation y = 50x + 100, where y is the cost of the plan and x is the number of months.
Step-by-step explanation:
To represent the cost of the mobile plan, we need to consider both the monthly cost of the plan and the initial cost of the mobile phone. Let y represent the cost of the mobile plan and x represent the number of months. The cost of the plan per month is $50. The initial cost of the mobile phone is $100. So, the equation that represents the cost of the mobile plan would be y = 50x + 100.