I agree with Michael that the question is probably expecting you
to estimate the answers from the graph. However, this is what I
would do if these were experimental results I was analysing.
Let's assume that the blue line is a straight line $f(x)$ and
the curve is a quadratic $g(x)$. A straight line has the form $y
= ax + b$ where $a$ is the gradient and $b$ is the $y$
intercept. From the graph the $y$ intercept is 1 and the
gradient is 4/10 i.e. 0.4. Then: $$ f(x) = 0.4x + 1 $$ The
quadratic is a little harder, but if you know the two zeroes of
the quadratic, $x_1$ and $x_2$ then the function has the form
$g(x) = A(x - x_1)(x - x_2)$ where $A$ is some constant. In our
case the two zeros are both $x = 5$ so the function is $g(x) =
A(x - 5)^2$. To find the constant $A$ note that when $x = 0$ $y
= 4$ so the constant $A$ must be 4/25 or 0.16. $$ g(x) = 0.16(x
- 5)^2 = 0.16x^2 - 1.6x + 4 $$ So to find the two values of $x$
when the curves cross we just set $f(x) = g(x)$: $$ 0.4x + 1 =
0.16x^2 - 1.6x + 4 $$ and a