Do 19-21
will mark brainliest

Question 19: x=9

Question 20: r<-6

Step-by-step explanation:

For question 19, the answer is nine because if you first add 5to both sides, it would be 18= 2r. If you divide both sides by 2, you would get 9=r.

For question 20, if you subtract 7 on each side, you would get -2r=12 if you divide -2 on each side, r would be -6.

the largest number of the four options is 1.8 x 10-2

you have it in scientific notation.

1.80 x 10-6   = 0.00000180

1.80 x 10-4   = 0.000180 (bigger, or "less small", than the former one)

so

1.8 x 10-2       = 0.0180. as you see. the "less small", or the biggest one of them all.

as you have negative exponent, it means you are dividing 1.8 by 100 (i.e. moving the dot towards left, two times).

if you had positive exponent for the scientific notation, power of tenths, you would be multiplying times 100 (moving the dot towards right) as below:

1.8 x (10)2 = 180

so. if you have negative exponent in scientific notation, move the dot toward left. if it is positive, toward right as many times the exponent tells you.

47 - 90 = 43

43 - 180 = x

x = 137