Let's see all the steps:
1) operation : 5 options
2) only one option: we ignore it
3) the third operation: 6 options
4): 2 options.
So we have 5 options, 6 options and 2 options: and they are independent of each other. This means that we multiply the numbers, and 5*6*2=60 So the answer is 60!
Answer:
a. 
b. x = 4 (see steps below)
Step-by-step explanation:
Since the two polygons are similar, the sides are proportional to each other. Using a proportion, you can solve for 'x' using cross-multiplication and division:

Cross-multiply: 15(x + 3) = 21(x + 1)
Distribute: 15x + 45 = 21x + 21
Subtract '15x' from both sides: 15x + 45 - 15x = 21x + 21 - 15x or 45 = 6x + 21
Subtract '21' from both sides: 45 - 21 = 6x + 21 - 21 or 24 = 6x
Divide by 6 on both sides: 24/6 = 6x/6
Solve for x: x = 4