Well fair enough, it's not all that easy to explain without a drawing, but good grief, it's only the 4 times table at worst ! And you'all have been at school doing basic math, since the age of 7 if not earlier ... I'm just not getting why it's so complicated, or maybe why UK math education is failing so badly.
How many inches in a foot ? Know ? Well, go look it up ! You've got the internet, and to be fair Ptaty, you're probably old enough to know there are 12 inches in a foot.
So 5 ft 10 is ( 5 x 12 ) + 10 = 60 + 10 = 70 inches.
Ok, now there are 4 inches in a hand (do they not tell you that at riding schools ? )... so how many sets of 4 inches are there in 70 inches?
You could, if you were real smart ( say - aged 7 ), do your 4 times table ... or ok, if you never learnt it just use your fingers and count off groups of four.
Seriously, try it. Draw a picture, write a spreadsheet, form a self-help group or whatever you need to do to be able to picture it, but good grief, it is NOT THAT DIFFICULT and if you're really struggling, put some effort into learning basic math (or borrow some fingers - I'm sure you can cobble together 7 friends whose fingers you could use to help with the counting).