Only number 3 and can u possibly use the substitution method

Ryan worked 3 hours mowing lawns and 7 hours with his dad.  

Step-by-step explanation:

This question is an example of a system of equations.  We can set up two equations using two variables and use the method of substitution to solve.  Subsitution involves solving for one variable and using this expression to substitute into the other equation.  In the case of Ryan, he has two variables the amount of hours he works for his dad (d) and the amount of hours he spends mowing laws (m).  In one week his combined hours is 10, so d + m = 10.  In the same week, he makes $84, or 6d + 14m = 84.  If we solve for 'd' in the first equation, we get d = 10-m.  We can then use this expression (10-m) to substitute for 'd' in the second equation:  6(10 - m) + 14m = 84.  Using distributive property and inverse operations, we can solve for the variable m:  60 - 6m + 14m = 84 or 60 + 8m = 84 or 8m = 24 or m = 3.  Since d + m = 10, d + 3 = 10 and d = 7.  

x= -3 and

step-by-step explanation:

to find the roots of a cubic, use division or factoring to find the factors then set equal to 0. as this is a difference of cubes, it factors into

where a is the cube root of .

here   this is 27 and the cube root of 27 is 3. so we write using the form:

.

set each factor to 0 and solve for x.

x-3=0

x=3

the quadratic expression does not factor and must be solved using the quadratic formula.

where a = 1, b=3, and c=9

this cubic has two complex roots.