Even the first one, 0.75 doubled and then doubled again is hard?
at this point in my life, as somebody with multiple math degrees, if i ever come across a situation where i need to multiply or divide numbers and one of them is bigger than 12, im going to use a calculator.
Look at Mr big brain over here who learned his times tables. Sure hope nobody takes his lunch money.

Shitty Math Pro Tip: If you ever have to work with numbers larger than 10, convert it to scientific notation and then round to a single significant figure.

? = 0.04 x 75 ? = (4 x 10^-2) x (7.5 x 10^1) ? ~= (4 x 10^-2) x (8 x 10^1) ? = 4 x 8 x 10^-1 ? = 32 x 10^-1 ? = 3.2 ? ~= 3

See how easy that is? Here’s another one:

? = 12 x 12 ? = (1.2 x 10^1) x (1.2 x 10^1) ? ~= (1 x 10^1) x (1 x 10^1) ? = 1 x 10^2 ? = 100

Bam, lock it in.

Depends on the sum though, like if its how many pizzas to buy you should round up.