
Answer:
y(x)  =  -0,25*x  + 2
Step-by-step explanation: If ice thickness decrease at a constant rate (for slope of a curve to be constant curve have to be a straight line.
Equation for straight line is
y(x)  =  m*x  + b
where y is tickness as function of time x is time, m slope  and b the interception with y axis
We need to find m  and b
b   when  x  =  0    y(x)  = 2  as from problem statement
therefore  b  =  2
After 3 weeks   y(x)  =  1.25
Then    1.25  =  m* (3)  + 2
3m  =  - 0,75
m  =  -  0,25
Finally Â
y(x)  =  -0,25*x  + 2