Start at 35 and start subtracting 4 (-4) then count each number so (35,31,27,23,19,15,11,7,3,-1) that’s 9 numbers so 1:00Pm +9 hours to 10:00PM and there you go
Combining like terms is simply representing them as a single term. With algebra, you can perform arithmetic on the coefficient (the 10 and the 4) to simplify the expression, giving you 6x.
