y = kb^x
lg y = lg kb^x
lg y = lg k + lg b^x
lg y = lg k + x lg b
lg y = (lg b) x + lg k

We need to plot lg y on the vertical against x on the horizontal

Gradient is equal to lg b
Vertical intercept is equal to lg k

(ii)

Once you obtain the gradient, lg b is the gradient. So let's say, for example, the gradient is 1. Then, lg b = 1, so that b = 10^1 = 10. I am only using this as an example since I would need to evaluate the actual gradient of the line. In your case, b = 10^gradient.

Similarly, lg k is the vertical intercept. Read off the intercept from your graph, and this will be your lg k. So, k = 10^intercept.

(iii)

From the graph, when x = 2.5, lg y = ...

Do graph tracing there.

lg y = ...
y = 10^(the reading you just obtained)

(iv)

Locate which is the worst point (the one which is far off the line)

Assume the x-value of that point is correct, find out the value of lg y of the graph for the x value you just identified

lg y = ...
y = 10^(the reading you just obtained)

thx:)