Which of the following has a graph that is a straight line?

Equation 1: y = 2x + 7

Equation 2: y2 = x - 1

Equation 3: y = 2x2 + 4

Equation 4: y = 3x3

Equation 2 is a square root function, kind of like half of a sideways parabola, Equation 3 is a parabola, and 4 is a cubic function (s-shaped). This leaves Equation 1, which is a line with a slope of 2 with a y-intercept at 7. So I'd say the answer is 1.