Maths in Focus is (too) easy but the questions might be a good starting point if you have trouble grasping a particular topic.
Other than that, Cambridge and Fitzpatrick are good as the others said - For whatever reason I found myself primarily using Fitzpatrick when I taught myself though.
Q2
P&=\text{ P rectangle +}\frac{\text{P circle}}{2} \\4&=x+2y+ \frac{x \pi }{2} \\y&= 2- \frac{x}{2} - \frac{x\pi}{4} \\ Area&=xy+\frac{\pi}{2}(\frac{x}{2})^2 \\ &=2x-\frac{x^2}{2}-\frac{x^2\pi}{4}+\frac{x^2\pi}{8} \text{ (subbing in y and multiplying through by x)} \\&=2x-\frac{x^2}{2}-...