I need help in understanding how to solve to get answer for some reason i can seem find a solution

Question

Why is the answer 123

1) X = (12)(13) (123)

Why is the answer 1875

18) X = (17)(15)(78) (1875)

Answer 1

x= 12(13) = 156

x=17(15)(78)= 19890

if you use the rule of 9's to check

add up the digits of each term

multiply them together 8(6)15) reduces to 8(6)(6) =48(6) to 12(6) to 3(6) = 18 which divides by 9

same with the product

as soon as you see the 9, that means the product's digits will also sum to a 9 divisible number

19890 is virtually certain to be correct,

1+9+8+9+0 = 36 reduces to 3+6=9

or at least it can't be excluded. about 90% chance you didnt' punch in the numbers incorrectly on a calculator

but 133 sums to 7 so it has to be a wrong answer

the product has to be evenly divisible by 9

while 1875 reduces to 1+8+7+5 = 21 reduces to 3, not 9

1875 has to be wrong