3(4r+5)-2(3r+4)=7
a. r= -1/3
b. r= 0
c. r= 1
d. r= 8/3

practice. practice. practice.

explanation:

infrared radiation has wavelength in the range between 700 nm and 1 mm. lets' convert these values into scientific notation, keeping in mind that:

let's start from the lower value, we have:

(we moved the dot two places to the left, so we increased the exponent by 2 units, from -9 to -7)

the higher value is:

so, the range of wavelength of infrared radiation is: