Calculating the gradient of a secant through points $x = 1, x = 1.5$ with equation $y = 2x^2 +1$

Question

I've checked my working, but my answer is not right. The correct answer is $5$.

My working:

$f(1) = 2x^2 + 1 = 2(1)^2 + 1 = 3$

$f(1.5) = 2(1.5)^2 + 1 = 4.5 + 1 = 5.5$

gradient = $(7 - 3) / (5.5 - 1) = (4) / (4.5) = 0.888$

Answer 1

hint

gradient = $$\frac {f (1.5)-f (1)}{(1.5)-(1)} $$

replace to find five.