The Diophantine equation $3x + 5y = 20$ has integer solutions. One particular solution is $(x_0, y_0) = (5, 1)$. The general solution is $x = 5 + 5t$, $y = 1 - 3t$ for integer $t$. How many solutions $(x, y)$ satisfy the equation AND $0 \le x \le 20$?