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.