A certain quantity is measured on two different scales, the R scale and the S scale, that are related linearly. Measurements on the R scale of 6 and 24 correspond to the measurements on the S scale of 30 and 60 respectively. What measurement on the R scale corresponds to a measurement of 90 on the S scale?	Pick one
A) 32
B) 36
C) 42
D) 48
E) 54
A change of +18 on the R scale is a change of +30 on the S scale.   R = (18/30)*S + K = 3S/5 + K   6 = 3(30)/5 + K   K = -12   R = 3S/5 - 12   R = 3(90)/5 - 12 = 54-12= 
<gadget id="calculator">54-12</gadget>
<output>42</output>
42   The answer is 42.
<result>C</result>
A certain quantity is measured on two different scales, the R scale and the S scale, that are related linearly. Measurements on the R scale of 6 and 24 correspond to the measurements on the S scale of 30 and 60 respectively. What measurement on the R scale corresponds to a measurement of 90 on the S scale?