We can take prime numbers so they don't have a common factor other than 1.
3, and 5.
So we have to list the multiples to find the LCM
3: 3, 6, 9, 12,
15, 18
5: 5, 10,
15, 20, 25
15 is the LCM of 3 and 5
So, you can notice that if two numbers, lets call them a and b, have no common factor, then

is the LCM.
Hope that helped :)
(2/5)+(3/(5x))=(x+5)/10
nasty fractions, we hates it forever
so
get rid of all those nasty fractions
multiply both sides by 10x
4x+6=x(x+5)
distribute
4x+6=x^2+5x
minus (4x+6) from both sides
0=x^2+x-6
factor
0=(x-2)(x+3)
set each to zero
0=x-2
2=x
0=x+3
-3=x
x=-3 and 2
3rd option is answer
X+12=26, x being the amount spent by Richard <span />
Answer: See photo posted below :)