To write a number in scientific notation, you need to write the number as a product of a number from 1 to under 10 multiplied by a integer power of 10.
First, what number from 1 to under 10 can you get out of the digits of 150,000,000 just by changing the decimal point? The answer is 1.5 since 1.5 is greater than or equal to 1 and less than 10.
150,000,000 = 1.5 * 100,000,000
Now we change 100,000,000 into a power of 10. A 1 followed by a number of zeros is the same as 10 to the power equal to the number of zeros. In 100,000,000 the 1 is followed by 8 zeros, so 100,000,000 = 10^8.
150,000,000 = 1.5 * 10^8