It's a bit hard to explain what I did for Question 10b ...
10b ii) I got 7/16 too!
Basically, you draw the two inequalities and have to find the area in between. Sub 1/4 into the inequalities, to find that they each hit x=1 and y=1 at 3/4. Then find the area of the two triangles (each is 3/4 x 3/4 x 1/2), and subtract them from the area of the square. i.e. 1 - (3/4)^2 = 7/16
iii) It's basically the same thing, only you have t/60 rather than 15/60. Sub t/60 into the inequalities to find that they hit x=1 and y=1 at 1- (t/60). Which means the two triangles each have the area of 1/2[1-(t/60)]^2. Therefore you have the equation: [1 - (t/60)]^2 = 1/2. Expand, factorise, and voila! I got 17 minutes 34 seconds, by the way.
I hope my explanation actually makes sense ...
I got 2018 for 8c)iii. Since you have to make the payment at the END of each year, you would only have paid 12 payments by the END of 2017. Therefore that tiny little bit would have to be paid in 2018. (Gah, am getting confused.)