OA

Red triangles are similar so use scale factor $\frac35=0.6$ to find missing lengths

Gradient is $\dfrac{4\times0.6}{3\times0.6}=\dfrac43$

AB

Green triangles are similar with scale factor $\frac45=0.8$

Gradient is $\dfrac{-3\times0.6}{4\times0.6}=-\dfrac34$

OA

Red triangles are similar so use large red triangle for the correct ratios

Gradient is $\dfrac43$

AB

Gradient is $\dfrac{-3}{4}=-\dfrac34$

You can find more short problems, arranged by curriculum topic, in our short problems collection.