If you were to use the substitution method to solve the following system, choose the new equation after the expression equivalent to x from the second equation is substituted into the first equation.
3x + 2y = −21
x − 3y = 4
a. 3(3y + 4) + 2y = −21
b. 3(−3y + 4) + 2y = −21
c. 3x + 2(3y + 4) = −21
d. 3x + 2(−3y + 4) = −21

An office supply company conducted a survey before marketing a new paper shredder designed for home use. in the survey, 80 % of the people who tried the shredder were satisfied with it. because of this high satisfaction rate, the company decided to market the new shredder. assume that 80 % of all people are satisfied with this shredder. during a certain month, 100 customers bought this shredder. find the probability that of these 100 customers, the number who are satisfied is 69 or fewer.