Question

Nereo and Azeneth start recording video at the same time. Nereo's phone starts with 1,000 megabytes

(MB) of free space and uses 7 MB of space per second of video.
Azeneth's phone has 1,255 MB of free space and uses 10 MB of space per second of video.
How much free space will they have when they first have the same amount of space left?

Answer 1

Create a system of equations
Nereo: y = -7x + 1000
Azeneth: y = -10x + 1255

Set equal and solve
-7x + 1000 = -10x + 1255
3x + 1000 = 1255
3x = 255
x = 85 seconds

Plug back in to find space left
-7(85) + 1000 = -10(85) + 1255
-595 + 1000 = -850 + 1255
405 = 405 MB