A slope field for an unknown differential equation has been sampled at lattice points. The slope at (0,1) is 2, and the slope at (1,3) is 4. Starting at (0,1), what is the best estimate of the y-coordinate of the solution curve at x=2 if two Euler steps of size Δx=1 are taken along those lattice points?
a) 5
b) 7
c) 3
d) 9