Answer:
Step-by-step explanation:
angle S+angle T+angle+angle R=180 degree(being sum of interior angle of a triangle)
4x^2-6x+40+18x+3+2x^2-7=180
6x^2+12x+36=180
6(x^2+2x+6)=180
x^2+2x+6=180/6
x^2+2x+6=30
x^2+2x=24
x(x+2)=24
x+2=24/x
x=24/x-2
x=24-2x/x
substitute the value of x^2 in angle R
2x^2-7
2(24-2x/x)^2-7(here x and x gets cancel)
2(24-2)^2-7
2*22^2-7
2*484-7
968-7
961
