y = 2x + c is given. Thus, we know immediately that the slope of this line is m = 2. If (k, 10) is a point on this line, then the following must be true:
10 = 2(k) + c, and
-3 + 2(0) + c
or
10 = 2k + c
c = -3
Thus, 10 = 2k + -3 becomes 13 = 2k, so that k = 6.5
