Question 1167309
From day 1 to day 6, Tim did 10 lunges on the first day and added 4 more lunges each day. So, on day x 

y = 4(x-1) + 10

Simplifying this equation, we get:

y = 4x + 6

day 7, y would be 0.

 the equation for the number of lunges Tim did for 7 days will be

y = 4x + 6(x-1)(x<7) + 0           (Day 7 0)

Simplify

y = 4x - 18 (x<7)
y = 4x(x-7) - 18