If it's add you subtract if it's subtract you add
Answer:
From the chapter Playing with numbers
we can define derek has 2×10^2 + 7 × 10^1 + 7× +0^0
as If ABC a number then ABC can be written as 10^2A+10^1B+10^0C
Hope it helps
See attached graph: v is on the y-axis and t is on the x-axis