Answer:

57

Step-by-step explanation:

Let:

t = tens digit

u = units digit

Given:

t + u = 12 (Equation 1)

u = 4t - 13 (Equation 2)

Find:

t and u (the number)

Strategy to be used:

Substitution method

Solution:

Substituting equation 2 in equation 1

t + u = 12

t + (4t - 13) = 12

t + 4t - 13 = 12

5t - 13 = 12

5t = 12 + 13

5t = 25

t = 25/5

t = 5

Substituting the value of t in equation 2

u = 4t - 13

u = 4(5) - 13

u = 20 - 13

u = 7

The number is 57

Checking:

in equation 1

t + u = 12

5 + 7 = 12

12 = 12 ✓

In equation 2

u = 4t - 13

7 = 4(5) - 13

7 = 20 - 13

7 = 7 ✓