Can you answer this seemingly simple algebra question?

The image has been shared and liked by more than 70,000 Facebook users and has attracted a whopping 480,000 comments.

"Concentrate because this is tricky - the correct answer is?" the post asks.

Answers have ranged from 22, 23, 44, 48 and 21.

**Most seem to agree the answer is 13 - here's why:**

x = horse

y = horseshoe

z = boot

x + x + x = 30

3x = 30

x = 10

x + 2y + 2y = 18

10 + 4y = 18

4y = 8

y = 2

2y - 2z = 2

4 - 2z = 2

-2z = -2

z = 1

x + y + z

10 + 2 + 1

13

**Others argue that the answer must be 21:**

It's 21!!

1 horse = 10 2 horse shoes = 4 (so 1 = 2) 2 boots = 2 (so 1 = 1)

1 + 10 x 2 ( apply BODMAS)

1 + (10 x 2) = 21

It's not the first time a maths question has caused confusion online. Earlier this year a question in a test designed for six-year-olds stumped adults who attempted it, and the internet had a meltdown over the seemingly simple intelligence test.