Answer:
a. DE = 15 cm
b. AB = 6 cm
Step-by-step explanation: Since these triangles are similar, you can find a factor that represents the corresponding side of one triangle to another. AC and CE are similar and both are given. AC is 1/3 of CE and CE is 3 time AC so those are the factors. To solve for DE we know that the length will be three times its corresponding side BC and therefore will be 15 cm. AB is one third of CD and will therefore be 18/3 which is 6 cm.