Answer: z = 280
Step-by-step explanation:
If two variables are directly proportional, it means that an increase in the value of one variable causes an increase in the value of the other variable. Also, a decrease in the value of one variable causes an decrease in the value of the other variable.
The variable z is directly proportional to x. If we introduce a constant of variation, the expression would be
z = kx
When x is 10, z has the value 140. It means that
140 = 10k
k = 140/10
k = 14
The equation becomes
z = 14x
the value of z when x = 20 is
z = 14 × 20
z = 280
