What percent
50% of 150% of x?

Convert both percents into decimals. To do that, move the percent sign two places to the left then multiply.

50% => 0.50
150% => 1.50
1.50 * 0.50 * x ; Start
0.75 * x            ; 1.50 * 0.50 is 0.75

The final answer is 0.75 * x. Which can also be expressed as 3/4x.